Claudia out late with boyfriend before she vanished, say police

The dramatic twist was revealed as more details of Miss Lawrence's complex private life were disclosed by North Yorkshire Police.

The York University chef is now thought to have been out with a boyfriend until at least 4.30am on March 17 last year – the day before she was last seen alive and only 90 minutes before she was due in work for an early morning shift.

On the eve of the first anniversary of her disappearance, it also emerged she had been having an affair for several months with a man who had a long-term partner at the time she vanished.

Det Supt Ray Galloway, who is heading the investigation, said officers were pursuing the "potentially significant" new lead to establish the identity of the man who was out with Miss Lawrence until the early hours. He also revealed she had managed to hide specific aspects of her life from even her closest friends and family.

Det Supt Galloway said: "She was able to compartmentalise her life with her work, hobbies, friends and family in a way most of us do not do. It is highly unusual as there is normally at least some crossover for most people.

"The curtains at Claudia's home were often closed, which can almost be seen as a metaphor for her life – when she went home, she closed the door to the outside world."

Police are trying to piece together whether the boyfriend she was with in York on March 17 was the same person with whom she had been having the affair.

But Det Supt Galloway stressed that early indications were that she had been involved with two different men. The latest disclosures will, however, only add to the heartache of Miss Lawrence's friends and relatives.

Her father, Peter Lawrence, 63, a solicitor from Slingsby in North Yorkshire, said: "As her father, I have always maintained that I will not necessarily know everything about Claudia's social life.

"At 36 years of age, it is up to her to make her own decisions – yes, I have met many of her friends but I accept that I may not have met them all.

"It is up to the police to investigate what they feel is relevant and, if this is a new lead to someone who was very close to her disappearance, I hope that person will come forward immediately."

It is understood there is no evidence to suggest Miss Lawrence was caught up in prostitution or illegal drugs, and officers do not believe that she was seeing a student from the university.

Details of her date until in the early hours of March 17 emerged when a colleague, who is also a friend, contacted police yesterday. He claimed he had asked Miss Lawrence why she looked so tired, and was told she had been out with the boyfriend until almost dawn.

Det Supt Galloway confirmed the man, who has been known to police since the inquiry began, decided to contact police as the first anniversary loomed. He admitted the delay was frustrating but refused to criticise the man for only coming forward 12 months after her disappearance.

Miss Lawrence was last seen walking near her Heworth Road home in York a year ago today and police upgraded the inquiry to a murder investigation last April.

Det Supt Galloway said the latest details to emerge about her private life were particularly important as they occurred so close to the time she vanished.