THE hunt for missing university chef Claudia Lawrence is being stepped up still further with a third nationwide TV appeal.

The search – already the biggest operation North Yorkshire Police have mounted in five years – will be featured on BBC TV’s Crimewatch again tonight, at 9pm.

The investigation will be the lead appeal on the show and the item will feature her family and friends, as well as the officers leading the hunt.

Listen to an excerpt from tonight's show

Miss Lawrence has not been seen since March 18, after leaving work at York University’s Goodricke College.

Despite a huge police operation, there has been no trace of the 35-year-old and detectives are officially treating the case as suspected murder.

The case was first featured on Crimewatch at the end of March, when it generated more than 100 calls from the public.

A second national TV appeal was made on April 10, when the mystery featured on BBC 1’s morning programme, Missing Live.

Tonight’s programme will include interviews with Miss Lawrence’s parents, Peter and Joan Lawrence, and her close friend Suzy Cooper.

Her distraught sister, Ali, will also be speaking for the first time about Miss Lawrence’s disappearance.

There will be reconstructions of her last known movements, as well as others of possible sightings that have since been reported to police.

The programme will also include shots taken within Miss Lawrence’s house, in Heworth Road, York, which has remained virtually untouched since her disappearance.

Her family have also released for broadcast home video of Miss Lawrence that was shot when she was a young girl, while police have provided a tape of her father’s initial call to them.

The man leading the inquiry, Detective Superintendent Ray Galloway, will be taking part in studio interviews.

The mystery surrounding Miss Lawrence’s disappearance has attracted attention all round the world.

National charity Crimestoppers has already taken the unusual step of offering a £10,000 reward in the case, and a website set up to assist the inquiry – findclaudia.co.uk – received 10,000 hits in a few days.

A police spokesman said: “Tonight’s broadcast will be the investigation team’s largest and most comprehensive appeal to date.

“We are hoping that the reconstructions, interviews and footage shown tonight will help jog people’s memories and provide that vital piece of information.”

He added: “There are still a number of unexplained sightings of people in the area at key times. We need these people to come forward and tell who they are.

“It could be they were there for entirely innocent reasons; however, we need to speak with them as they could have vital information that could help lead us to Claudia and those responsible for her disappearance.”