THE detective leading the hunt for university chef Claudia Lawrence today revealed a motorist saw a couple involved in a roadside altercation hours after the missing 35-year-old was last seen alive and well.

Detective Superintendent Ray Galloway told reporters in York it was a significant line of inquiry with Miss Lawrence now missing for more than four weeks.

Miss Lawrence was last seen on March 18 after she finished work at the University of Yorks Goodricke College and has not been in contact with anybody since about 8.30pm that day.

Police fear she may have come to harm after meeting someone she knows.

Mr Galloway said the motorist was driving towards the university along University Road when he came across the couple at 6.10am on March 19.

He said the car, which he does not have a description of, was parked on the left-hand side with a passenger door open.

The witness told police he saw a couple on the other side of the carriageway involved in some form of verbal argument.

Mr Galloway told reporters in York: "The man and woman appeared to be in some form of altercation. We think it was a verbal altercation.

"He drives past and, as he looks in his wing mirror, his rear view mirror,he actually believes the man is stood above the woman i.e. as if he is on some form of banking.

"It's a significant line of inquiry which we wish to pursue.

"Were you that person? Were you involved in that vehicle? It could have been someone just dropping off their partner, their friend, their son, their daughter and it's just an argument thats taking place.

"There might be an innocent explanation."

The detective said it was possible it wasnt Claudia and he had no description of the couple involved.

However, he said it was a key moment for the inquiry team as it was the morning Miss Lawrence was due to turn up for work at the university.

Mr Galloway also revealed that, on March 10 or 13, a woman motorist passing by Miss Lawrences home on Heworth Road in slow moving traffic saw two men outside the chefs front door.

One was described as an Asian male, while police have no description of the other man.

Mr Galloway added: "We obviously need to know who the men are.

"The detective said the Asian male seen at Miss Lawrences front door was described as aged in his early 20s, 5ft 8in tall, of slim build and with a thin, pointed nose and dark areas beneath his eyes.

"He was described as nervous. The second man was taller, with dark hair and a heavier build. He was described as wearing a Crombie-style coat.

"They were seen outside the front door in the early afternoon. One of the men appeared to be trying the door, either with a key or by turning the handle."

Mr Galloway urged anyone with any information to contact the inquiry team.

He also referred to Facebook, saying: "There is a significant amount of people who are contributing to that site.

"Now some of them are making what could potentially be useful information appeals or claiming that they have information that could be useful to the investigation.

"I don't have the ability to identify who they are.

"Some of them are by nickname, some of them are completely anonymous.

"I would urge anybody that has any information that they are imparting on the Facebook site, please use the police hotline and contact us and allow us to contextualise the information and help take it forward."

Mr Galloway was asked if Miss Lawrence may have a more complicated private life than her friends and family were aware of.

The detective said he had no evidence of a new relationship, but he was keen to hear from anyone who had any information about her private life.

He stressed he was there to investigate, not judge, and appealed for people to come forward.

Asked how concerned he was for her wellbeing, he said he had significant concerns for her safety.

The North Yorkshire police investigation into Miss Lawrences disappearance is now the biggest the force has conducted since the search for multiple killer Mark Hobson five years ago.