'Come forward' plea by missing Claudia's family

On the anniversary of her disappearance, Miss Lawrence's father Peter said he could not believe that despite being missing for 12 months people were still coming forward with vital information, while her mother Joan spoke of her ongoing pain at not knowing what had happened to her.

Yesterday marked the anniversary of the day Claudia went missing and saw the new revelation she was out almost until dawn with a mystery man two days prior to her vanishing.

Police also disclosed she was involved in a long-term, casual sexual relationship with another man when she vanished.

The man was himself involved in a long-term relationship with another woman but is not believed to be the boyfriend Miss Lawrence was with on March 17 last year.

Her mother Joan said she knew nothing about a mystery boyfriend and would consult her diaries to see if they contained any new clues.

Miss Lawrence's sister, Ali Sims told GMTV: "I know that some people, if they were in a relationship and had a relationship with Claudia...I am sure they will want to save their existing relationship. But I think they should put that aside..they need to come forward."

In a separate interview Miss Lawrence's mother Joan said: "I miss her terribly. I just can't tell you how much I miss her. The emptiness... there's just that gap."

In a Press conference in Leeds, Mr Lawrence, who has led the campaign for information on his daughter, expressed his disappointment that people were still volunteering vital information so long after she disappeared.

Details of her date had emerged after a friend and work colleague contacted police ahead of the one-year anniversary. Detectives confirmed the man had been known to them since the inquiry began but would not criticise him for the delay in coming forward.

Mr Lawrence said: "It is unbelievable that someone who has already been interviewed by the police has suddenly remembered that they had a conversation with Claudia before she disappeared."

And he urged people to cast their minds back to a year ago to see if they could help with the investigation.

He said: "Somebody out there has this valuable piece of information. We had St Patrick's Day and Cheltenham which will be in various people's area of interest and it was at this time that Claudia disappeared.

"Everybody out there is a parent themselves or are very close to somebody who is a parent – they must know what we are going through. If anyone has any information, please give it.

"I do believe she is alive. I would have felt differently if she had been dead."

Mr Lawrence added he was feeling drained following the past few days and the campaigning to find his daughter had taken its toll but said the support of his friends, family and the general public had been of great comfort to him, including well-wishers who regularly stopped him in the street.

"It is a dreadful situation for somebody to be in," he added. "I am missing a great part of my life but I will keep going."

Det Supt Ray Galloway , who is leading police inquiry, described the new information about Miss Lawrence as "extremely hot intelligence" and said it was "critical" they spoke to the man whom Miss Lawrence was said to have been with until the early hours of the morning of March 17 last year.

Det Supt Galloway said: "Critically, information has come to us only today whereby we understand that Claudia has told (someone) that she was actually out on one of the evenings, on one of the nights which immediately preceded her disappearance – out into the very early hours with what she described as a boyfriend and we are talking deep into the night, half past four or five o'clock in the morning."

He added there was "nothing suspicious" in the new information but the man would need to be identified so he could be eliminated from the investigation.