Prince George was back in class today after after a suspected stalker was arrested for twice attempting to break into his £20,000-a-year prep school twice in 24 hours.
The future king was swept into Thomas's Battersea in a convoy of blacked-out Range Rovers - but it appears Prince William and Kate stayed at home.
A major security review was launched last night and Scotland Yard is working with Thomas's Battersea following a scare experts have called an 'unacceptable breach of security'
Teachers were on red alert after the same woman had been able to briefly talk her way into the building posing as a legitimate visitor a day earlier.
She escaped when challenged by staff but was spotted again loitering nearby triggering her arrest on suspicion of attempted burglary.
The woman was being questioned at a south London police station last night and one line of inquiry is that she is a 'fixated individual' who has become obsessed with the glamorous Royal couple.
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These exclusive pictures reveal the moment police arrested the woman as she sat outside Queenswood restaurant in Battersea Square with two men, one believed to be an undercover police officer
Prince George had his first day at Thomas's Battersea School last week - he was back in school today after the security scare
The prince, four, who is third in line to the throne, was not present at the time of either security scare because as a new starter he leaves at lunchtime.
Today he arrived in a black Range Rover driven by an unknown man and with a female passenger. The gates to the courtyard were briefly lifted to allow the prince into school before the 4x4 drove away.
George's car was tailed by a second Range Rover which appeared to be driven by a plain clothes police officer. His parents did not appear to be there.
Parents remained tight-lipped about the security scares.
One parent said: 'The school have been very clear. We have all been told not to say anything or talk about anything.' Others ignored questions about safety at the school.
The woman was sitting outside Queenswood restaurant in Battersea Square with two men, one believed to be an undercover police officer, when the arrest operation began.
At 2.20pm, an unmarked police car sped into the square followed by a police van which stopped outside the restaurant.
Three police officers, two male and one female, spoke briefly to the woman. She was then searched by the female officer before stepping into the back of the van.
She remained composed throughout and did not remonstrate with the officers.
One eyewitness, who was eating at the restaurant, said: 'She was just sitting there really quietly with two men in ordinary clothes either side of her. She was completely calm and passive. She seemed completely unfazed.'
Commanders at the Metropolitan Police's Royalty and Specialist Protection Unit launched an immediate review of the security operation surrounding his studies.
But the incident will raise fears of what could have happened had the woman been a terrorist.
One former senior officer last night described the shocking breach as 'very worrying', but added: 'Schools are not fortresses.'
The prince only started his studies last Thursday when he was photographed being dropped off at the school by his father, the Duke of Cambridge.
The Duchess of Cambridge, who is pregnant with her third child and has been suffering from a severe form of morning sickness, told parents she will meet them at the gates when she, too, is able to do the school run.
The security incident involving the woman began unfolding on Tuesday afternoon.
It is understood that she attempted to gain access to the school by posing as a visitor, possibly with a pre-booked appointment.
But she quickly left the building, which opens directly onto a busy road, after being challenged by a member of staff. It is unclear how far inside she got.
Shortly before 2pm yesterday the woman was seen again in a small leafy square a short distance from the school gates.
Police were alerted and she was held by plainclothes officers until uniformed colleagues arrived to search and arrest her.
One eyewitness, who was eating at Queenswood, in Battersea Square, said she was alerted by two 'very agitated' teachers wearing distinctive name badges standing outside.
The 40-year-old woman was detained by undercover police officers yards from the gates of Thomas's London Day School in Battersea, south-west London
She realised that a woman had been made to a sit at a table at an adjacent cafe and was surrounded by two men in civilian clothes.
'She seemed very placid, completely unfazed by what was going on,' she said. 'She was silent and did not exchange anything with police at all. She had light dark hair in a ponytail and had a rucksack-type bag over her shoulder.
'A woman officer arrived and searched her and then she stepped into the back of the police van.
'There were several Thomas's staff wearing name badges who looked very agitated. I saw them being shown some passports or a passport. It made me think the woman could be from overseas.'
The woman was being questioned on suspicion of attempted burglary at a south London police station last night. Her mental health will be assessed.
One line of inquiry is that she is a 'fixated individual' who has become obsessed with the glamorous Royal couple.
Many security experts believe such people pose a greater threat to the Royal Family than terrorists because they are often unpredictable loners.
Prince George, third in line to the throne, is dropped off by William as he arrives at the the £18,000-a-year school last week
Questions were raised over security at Thomas's earlier this month after a woman was able to video herself walking inside it.
Battersea resident Sarah Burnett-Moore, 54, filmed inside the £18,000-a-year school while it was being refurbished over the summer. It appears she was able to enter the premises via the same iron gate and main door after they were left open by contractors.
She said she could have walked in with a home-made bomb and many neighbours of the school are concerned about the security implications of the royal pupil.
Residents said they are concerned that security at the school is not adequate for the high-profile pupil. One mother, aged 39, said: 'Incidents like this make us all scared. Prince George shouldn't go here. None of the mums around here want him to go to the school because it's putting us locals and our children under threat.
Prince George arrives for his first day of school with his father Prince William, Duke of Cambridge, as they are met head of the lower school Helen Haslem
'The school needs better security and gates. Anyone can walk in. I walk past and can just walk inside whenever I like if I wanted to.'
In contrast another woman added: 'I didn't feel safe before, but now Prince George is at the school I actually feel a lot safer. It means there is more heightened security than there was before.
'I was mugged just down the road and it's one of those places that is one extreme to the other.'
Chris Phillips, the former head of the National Counter Terrorism Security Office, said 'It does not surprise me,' he said. 'Schools are public places, they have never been fortresses,' he added.
'It's very worrying when you get incidents like this. But don't forget Buckingham Palace has had a number of break-ins and that is pretty much a fortress. Whenever George is there are usually armed police there too.'
He added that the duke and duchess must balance leading ordinary lives with their security.
Scotland Yard said: 'Police were alerted and officers attended immediately after the issue came to light. We are working with the school to review its security arrangements after the incident.'
A Thomas's spokesman said: 'We are unable to comment due to the ongoing police investigation into this incident.'
What if it had been a terrorist? Ex-royal protection officer KEN WHARFE says there's no excuse for the unacceptable security breach at George's school
By Inspector Ken Wharfe, former royal protection officer
That an intruder can walk in to Prince George's school from the street before being challenged raises serious and urgent questions, writes Inspector Ken Wharfe
This was a completely unacceptable breach of security. That an intruder can walk in to Prince George's school from the street before being challenged raises serious and urgent questions.
It doesn't matter how long the person was on the premises. What counts is how far they penetrated – and no one should be allowed to get access to any part of the school building. It's as simple as that.
The fear of someone roaming inside Thomas's does not bear thinking about. Thankfully on this occasion the intruder was intercepted before she could go any further. But suppose it had been a terrorist intent on killing? By then it would have been too late. That this person was able to reach reception was far too close for comfort.
For royalty protection, however, this is a wake-up call. George has been at the school only five days and already elaborate plans to protect him have been compromised.
Before I became personal protection officer to Princess Diana, my task was to head the security around William and Harry. It therefore fell to me to ensure William's safety at school when he began at Wetherby Prep in Notting Hill in 1987 at the same age George is today.
I understand that the template we developed there three decades ago is very much the one that has been adopted by those whose job is to guard Prince George.
Which raises the question: how could things have gone so wrong? It is only fair to point out that Thomas's, with nearly 600 pupils, is different from Wetherby, which was then a small school with far fewer children.
William appreciated the low-profile policing that accompanied him throughout his school days and wanted it to be replicated for George. This means no burly bodyguard in the classroom or an officer with him every time he wants to make a call of nature.
Had there been a suggestion from officers, for example, to post police outside the school gates, I know William would have vetoed it. He not only wants his son to have as normal a school experience as is possible, but also his school mates – which means keeping the protection low key.
No one should be allowed to get access to any part of the school building. It's as simple as that, writes Inspector Wharfe
But that is no excuse for the kind of breaches that happened not once this week, but twice.
Unfortunately the world is a far more dangerous place than it was 30 years ago. We live in an era of unpredictable international terrorism that can strike at any time. The publicity for an attack on a member of the royal family would be incalculable.
It means those guarding the prince, even at school, cannot afford to ever let things slip. They must be prepared for terrorists and those sad individuals with dangerous fixations about the royals.
At Wetherby we had a strict and successful routine. Long before either William or Harry, when he later joined him, arrived each morning, a specialist with a sniffer dog searched the school. This happened every day. Only when they were satisfied the school was safe was I signalled and we left Kensington Palace for the short drive to Wetherby. Inside the school I set up an operational room where my colleagues and I were based.
I understand this has similarly been done at Thomas's, where CCTV pictures of George's classroom are relayed to his officers, whose room is close enough for them to respond to an incident in seconds. There are also elaborate alarms in place.
Because the terrorist threat is so much higher now, I believe George has a team of four close protection officers guarding him on a daily basis. It is likely there may also be back-up provided by police in the local Battersea area. If so, questions must be asked about securing the perimeter of the school.
No one wants to see the royals cocooned in the kind of security bubble that surrounds figures such as the US President, but also nobody wants to see any member of the royal family at risk from the deranged or from terrorists.
Something clearly went wrong yesterday. Mercifully there were no consequences. But changes in protecting George will have to be made.
- Ken Wharfe is a retired Metropolitan Police inspector who was a bodyguard for Princess Diana and Prince William