DAVID Cameron yesterday took full responsibility for a security breach that resulted in his eight-year-old daughter being left behind in a country pub.

The Prime Minister's spokeswoman said there would be no inquiry, and no member of his security team would face disciplinary action.

David and Samantha Cameron had gone to The Plough at Cadsden, Buckinghamshire, in April for Sunday lunch with their children Nancy, Arthur, six, and 22-month-old Florence, with two other families and their children.

On leaving, the Prime Minister and his family, together with security officers, their friends and their children got into a number of vehicles.

It is believed Nancy wandered into the pub's lavatory while they were arranging the lifts back to Chequers.

The spokeswoman said Mr Cameron and his wife were distraught when they arrived back at their country residence in Buckinghamshire to discover Nancy was not with them and was still two miles away at The Plough.

The pub was then phoned and their daughter was retrieved.

The spokeswoman said: "There was a mix-up. Samantha thought the Prime Minister had Nancy and the Prime Minister thought Samantha had Nancy."

The spokeswoman insisted the Prime Minister had simply made a mistake and that there would be no official inquiry.

Asked why Mr Cameron's protection team had not taken a headcount, she made clear she would not go into the details of his security arrangements but explained these were kept under constant review.

She said: "The Prime Minister is a very busy man but he always tries to live as normal a life as possible with his family."

Asked if he took 100% responsibility for leaving Nancy behind, she replied: "You can make that assumption."

She added: "They are their children and they take responsibility for them. No-one is going to face disciplinary action. This was an error."

A Plough source revealed Nancy had been found in the toilet, adding: "You'd have thought someone would have done a headcount or something.

"It's not like you can look up David Cameron in the phone book and then ring him to say 'You've left your daughter behind'."

The development has led to a number of families admitting to similar incidents, with some suggesting their mistakes had resulted in a visit from social services.

Asked if that had happened to the Prime Minister, his spokeswoman replied: "No". She added: "It was clearly a one-off issue."