The apology from Dan Corry, a former transport department special adviser, comes after news that he sent an e-mail trying to discover the political sympathies of the Paddington rail crash survivors' group.

I can't believe our prime minister can sit there and say he cares about the people he is governing, then ignore us totally

Pam Warren, Paddington rail crash survivor

Tony Blair has expressed his "regret" over the affair and the government insists the e-mail, which was sent as then Transport Secretary Stephen Byers came under fire from the group, should not have been sent.

The Conservatives say the debacle is part of the government's desire to "smear" its critics and is a "disgrace".

Officials stressed the memo was not about Pam Warren, the previous survivors' group leader who later accused Mr Byers of misleading Parliament a day before the memo was sent.

Saying sorry

Mr Corry is in Japan to watch the England-Argentina football match, where he is apparently being stalked by camera crews.

In a statement issued by the Labour Party, he said: "It was wrong of me to send these e-mails.

"I would like to apologise unreservedly to the Paddington Survivors Group, Pam Warren, the relatives involved and to anybody who has taken offence at this."

Pam Warren says Blair's "regret" is not enough

Both Mr Byers and his successor Alistair Darling have already apologised for the incident, saying they knew nothing about it.

Mr Corry tried to establish whether the people taking over the helm of the Paddington Survivors' Group of rail crash victims had any known political links.

"Basically, are they Tories?" he asked about those on the group in an e-mail to Labour headquarters.

Attacking critics

Conservative Party chairman David Davis told BBC Radio 4's Today programme the e-mail was an attempt by Labour to smear its critics.

He said it was one of several similar incidents, citing attacks on Rose Addis, the elderly patient whose complaints last year sparked a political storm.

"What they indicate is a government that rather than respond to criticism by putting right the problem, looks for a way of attacking those who criticise it," said Mr Davis.

Charles Kennedy called the e-mail "obnoxious"

Meanwhile, Liberal Democrat leader Charles Kennedy called the memo "obnoxious".

Downing Street said Mr Blair had known nothing about the e-mail but shares the regret that it had been sent.

That was not enough for Mrs Warren, who demanded a personal apology from the prime minister.

Shock

"I can't believe our prime minister can sit there and say he cares about the people he is governing, then ignore us totally," she said.

Simon Benham, the new chairman of survivors' group who was named in the e-mails, said he was shocked and sickened by the affair.

He told BBC Radio 4's Today programme he had no political affiliations.

But Martin Minns, the Survivors' Group public relations adviser also mentioned in the e-mails, has confirmed some links with the Conservatives - but said it was irrelevant and that his membership had lapsed.

'High opinion'

Mr Minns told BBC Radio 4's The World at One he had been a party agent and assistant campaign director at Conservative Central Office before setting up his own company.

He said: "I do think it's very concerning that we can say just because somebody may be a Liberal, a Conservative, a Labour Party supporter, that they are not in a position to do a professional job as an adviser."

Former Northern Ireland Secretary Peter Mandelson came to Mr Corry's defence, telling the programme: "I have the highest opinion of him.

"I cannot think of anyone less likely to be involved in politicising something like this."

Misled

It was the e-mail from former special adviser Jo Moore suggesting 11 September was a good day to bury bad news that prompted much of the controversy leading to Stephen Byers' resignation last week.

Mrs Warren, 35, a financial consultant, claimed last month that Mr Byers misled MPs over Railtrack, something the ex-minister denies.

Labour MP Tony Wright, who chairs the Commons public administration select committee, said Mr Corry had a good reputation as a policy adviser and was not a spin doctor.

But the problems that had built up in the department had meant "everyone was sucked into this defence operation", he told Today.

Dr Wright suggested, however, that the survivors' group had lost moral authority by entering the political row over the reorganisation of Railtrack.