Labour sent the Health Secretary John Reid on a flying visit to the key marginal seat of Dorset South today to press for the prospective Tory parliamentary candidate to be sacked in a row over doctored photographs.

Mr Reid condemned as a "sick stunt" the actions of Ed Matts, whose campaign leaflet includes a photograph of him and Ann Widdecombe holding placards apparently calling for limits on immigration and asylum.

But the original photograph showed Mr Matts and Miss Widdecombe campaigning for a Malawian family of asylum seekers to be allowed to stay in Britain.

Today Mr Matts apologised for changing the photo, which he described as a mistake. Mr Howard, the Tory leader, said that he did not intend to force Mr Matts to resign - unlike his draconian action against Howard Flight, the former Conservative deputy chairman, who was sacked for suggesting that the Tories had a secret spending-cuts agenda.

But Mr Reid insisted that Mr Matts should go, saying that if Mr Howard failed to sack him he would be sending out a message to other candidates that they can "do anything they like to fuel a wholly negative campaign".

"To pose in one picture in support of an asylum seeker, and then doctor the same picture for a political stunt is sick," he said.

"Mr Matts is a disgrace to Dorset, a disgrace to politics, and would be a disgrace to Parliament if he were ever elected."

In an impromptu press conference in Dorset South he added: "Defending deceit and duplicity on this scale can only mean Michael Howard’s whole intention is to exploit the immigration issue not deal with it."

Menzies Campbell, the Liberal Democrat deputy leader, agreed: "Howard Flight was sacked by the Conservatives for telling the truth. Ed Matts should be sacked for telling lies."

Mr Howard said today, on a visit to Torquay, that Mr Matts had been in the wrong but there was no need for him to share Mr Flight's fate. He said: "No, no, not at all. He has apologised. He should not have done what he did but he has apologised."

He insisted the incident was not a sign of wider confusion in the party about the issue of immigration, which has so far generated a heated debate in the election campaign.

Trevor Phillips, the head of the Commission for Racial Equality, said in an interview with The Times today that the parties were inflaming ugly tensions in society, and described the atmosphere as sour, fractious and brittle. The commission has been deluged with reports of racist violence in the past month, he said.

"I am probably the most worried person in the country at the moment," said Mr Phillips. "We want politicians to calm down, take a step back and realise what their words - and the tone of their words - may do to people on the ground...

"If someone gets badly hurt during this campaign, all those people using this sort of language will have to ask themselves if they contributed to it."

When The Times approached Mr Matts last night, he at first claimed that there had been two photographs, but later he admitted that he had changed the picture. He said that he did it because voters would not understand Tory policy is for "controlled immigration" and "humane limits on asylum applications", and insisted: "I don't think there is anything wrong in what I'm doing."

In his statement today he says: "I apologise for making a foolish mistake - I had no intention of causing any embarrassment.

"However, being involved in an individual asylum case is not inconsistent with the Conservative view that Britain’s asylum system is in urgent need of attention."

Miss Widdecombe, a former Tory Home Office minister, said that she had no qualms about being associated either with Tory asylum policy or with the campaign to allow Verah Kachepa and her four children to stay in Britain.

"Ed Matts did not ask me for permission to change the photo and if he had told me he was going to do it that way, I would have advised him against," she admitted.

"Now I associate myself entirely with both messages that are shown, but it was a very ill-advised way to do it because it laid itself open to misinterpretations."

She added however: "Ed Matts should not be sacked."

Mrs Kachepa said she was unhappy at being used as a tool for party political campaigning, and criticised Mr Matts for changing his tune.

Dorset South is number three on the Conservatives’ list of target seats for May 5. The Tories need a swing of only 0.17 per cent to overturn Labour MP Jim Knight’s 153 vote majority.

Times Recommends

• Brown gambles it all on rescue plan
• Motherhood boosts female brain power
• That's no old FT, that's my naked wife