The incident in Leeds today where a man was able to run into David Cameron on the street has raised questions about security arrangements for the prime minister.
While most British politicians prefer not to be surrounded by a "ring of steel", the incident has prompted an investigation by the Metropolitan Police, which is responsible for Mr Cameron's safety.
ITV News political correspondent Libby Wiener reports:
A runner who collided with the Prime Minister prompting security concerns has told the BBC he "did not see him."
Dean Farley said: "I didn't see David Cameron. I didn't know it was David Cameron until they let me out of the police van an hour later and told me what I'd actually done."
He said he asked the officers repeatedly what he had done as he was detained in the van and one officer said to him: "You know what you've done, be quiet."
"I gathered I'd run into somebody quite important but I couldn't know it was David Cameron. It begs the question, how good is Cameron's security if I managed to run between it before they stopped me?", Mr Farley added.
Mr Farley denied the collision was some sort of protest, adding that he was "not a particularly political-minded person".
David Cameron insisted he has confidence in his protection detail after a runner collided with him during a visit to Leeds.
The Met Police announced it will carry out a review into the incident, which some MPs have called a "clear breach of security".
ITV News Political Correspondent Libby Wiener reports:
The man who collided with David Cameron while running has said he just brushed into someone.
"Next thing I know I've got half a dozen suited men haranguing me and manhandling me to the floor," Dean Farley told the BBC.
"The whole time I'm asking, 'who are you, what's going on?'" he added.
The mother of the man who collided with David Cameron earlier today said he was "very upset by the whole situation".
Dean Farley's mother said she had spoken to him and that it was "all a misunderstanding."
"He was just jogging to the gym," she said, adding, "That's all I've got to say."
A witness to the incident involving David Cameron in Leeds today has described how the Prime Minister "sidestepped" the 28-year-old man in a "lovely little move".
Chris Wilson said: "It looked like Cameron sidestepped him. It was a lovely little move. He should be on the stage, really. And then he was tackled by the person behind. And then he [Cameron] was in the car and the car was gone."
He added: "They were on him. They were like flies round poo. One minute he was down, then he was up again and moving. It was fast."
He ran about 10 yards across the road towards the Prime Minister, who looked around, but did not seemed worried, Mr Wilson said.
Dean Farley later said on Facebook that he was the man involved in the incident.
David Cameron has insisted he has confidence in his police bodyguards after a runner collided into him and his security detail earlier today.
"Could I put on the record for once the debt I owe to the close protection teams that look after me and the very good job that they do," the Prime Minister told MPs during a scheduled statement.
Making light of the incident, Cameron added: "John Prescott was in the room as I gave the speech so as I left the room, I thought the moment of maximum danger had probably passed.
"But clearly that wasn't the case."
The man who was arrested after a collision with the Prime Minister has said he was only guilty of "brushing into someone while running".
Dean Farley wrote on his Facebook page: "So I'm all over the news as 'the protester that attacked David Cameron in Leeds.'
"Yeah if you call brushing into someone while running then getting assaulted by half a dozen coppers in suits attacking."
The Metropolitan Police will conduct a review of the incident in Leeds involving a 28-year-old man and David Cameron in consultation with West Yorkshire Police.
The Met's Specialist Protection Command is responsible for the personal protection of the Prime Minister.
The Met confirmed that the man, who shoved Mr Cameron as he left the Civic Hall, had been arrested and later de-arrested by local officers.
Tory MP Mark Pritchard has demanded a full investigation into how the Metropolitan Police security team allowed a man to get so close to the Prime Minister in Leeds today.
He called for the Met's commissioner Sir Bernard Hogan-Howe to launch an immediate internal inquiry.
The Met Police have some of the best close protection officers in the world.
However, this was a clear breach of security and could have been far more sinister in outcome.
With the terror threat level increased, this cannot be allowed to happen again.
The Met Commissioner should call an immediate and swift internal inquiry to discover why this happened and implement the necessary lessons learned as quickly as possible.