A convicted paedophile was employed as a nurse on a children's ward at Northwick Park Hospital, it has been revealed.
Lars Gellner, 37, had been convicted by a court in Cambodia for a string of sex attacks on young boys but managed to get through security checks in the UK.
The North West London Hospitals Trust, which manages the hospital in Watford Road, says a criminal record check was carried out on Gellner by an agency but because he had no criminal record in Europe he sneakily got the job on Jack's Place in October last year.
The German was finally caught after applying for a UK visa for a 14-year-old Burmese boy he wanted to bring here for a holiday.
An official from the British embassy recognised his name from reports and a police sex offender unit traced him to Northwick Park Hospital where he was arrested on duty.
Detective Sergeant Sam Hayward said: "Our team have stopped this man creating more child victims in this country.
"No blame should be attached to the hospitals. They did everything they could to carry out the criminal checks on him and they came back showing nothing."
Documents from a Cambodian court claim Gellner spent years preying on youngsters in the Far East and was suspected of raping a boy aged 10.
After he was arrested in October he was placed on the sex offenders register and charged with fraud for failure to include his criminal record on his job application.
He appeared at Aylesbury Crown Court on Thursday (feb 26) last week but Judge Christopher Tyrer was forced to throw the case out because of a problem with documents sent from Cambodia.
He is currently being held in custody until the UK Border Agency decides what to do with him.
A spokeswomen from North West London Hospital Trust said: "The Trust can confirm that Mr Gellner worked a small number of shifts at Northwick Park Hospital in October 2007.
"He was employed through an agency and we can confirm that they conducted an enhanced Criminal Record Bureau (CRB) check. Our contracts with employment agencies stipulate that CRB checks must be carried out on staff supplied to us. "