Damian McBride was forced to quit over smear e-mails
Damian McBride, the Downing Street aide forced to quit over e-mails smearing top Tories, has "disappeared without a trace", a senior Labour MP has said.
Tony Wright said he had wanted Mr McBride to give evidence to the Commons public administration committee.
He "seems to have disappeared without a trace and despite our best endeavours we haven't been able to trace him", committee chairman Mr Wright said.
The committee is investigating the role of special advisers in UK politics.
Mr Wright said it would continue its efforts to contact Mr McBride.
The former Downing Street adviser has not been seen in public since he was forced to quit over e-mails discussing plans to spread unfounded stories about leading Conservatives.
He was sacked by Prime Minister Gordon Brown without compensation and is reportedly currently unemployed.
Derek Draper, another key figure in the e-mail row, earlier quit as editor of the LabourList blog.
Mr Draper had been discussing plans with Mr McBride to set up a separate gossip website, Red Rag, to counter the perceived dominance of Tory-supporting blogs.
In one leaked e-mail, Mr Draper described Mr McBride's plan to spread unfounded rumours about senior Conservatives as "absolutely totally brilliant".
But in a resignation statement e-mailed to LabourList subscribers, Mr Draper said: "I regret ever receiving the infamous e-mail and I regret my stupid, hasty reply. I should have said straight away that the idea was wrong."
But he said his continued editorship of LabourList "can only detract from what Labourlist needs to do now". He will be replaced by his deputy Alex Smith.
Gordon Brown pledged to tighten up the code of conduct for special advisers - backroom staff employed to give political advice and brief the media - following the smeargate row.
But the public administration committee has launched an investigation into their activities and whether they should continue be funded by the taxpayer rather than the political parties.
Jonathan Baume, general secretary of civil service union the First Division association, told the committee Damian McBride became a special adviser after concerns he was becoming too political in his role as a civil servant at the Treasury, where he had been one of Mr Brown's closest advisers.
But he said there was no need for wholesale reform of the special adviser system.
Sir Richard Mottram, who was the top civil servant at the Transport department during a previous row about special advisers - when Jo Moore said September 11 2001 was a good day to bury bad news, said ministers had been warned about Mr McBride.
"It wasn't a great surprise that a problem arose about him. It was a risk that I think was seen," he told the committee.
He called for a crackdown on the number of special advisers, which has grown under Labour, and a rethink of their role - including an end to their wages being paid by taxpayers.
He also described the beer and football-fuelled atmosphere at the top of government, which he said led to the spreading of smears and gossip.
"The whole culture is very laddish and exclusive in the sense of pushing people people out. It is not desirable to have a taxpayer-funded version of it spreading poison in the media," he told MPs.
Former Labour special adviser Lance Price told the committee he discussed the sex lives of political opponents with Tony Blair when he was prime minister.
But he said it was just "gossip" and unlike the email smears of Gordon Brown's former adviser, Damian McBride, it was never made public.
He told MPs: "The number of occasions that I might have had of that sort with the prime minister were very few.
"They might have been at the end of a long day. They might have been when we were on a plane somewhere, when we were relaxing and chilling out, having spent an awful lot of time at the public's expense working on policy and serious issues that we were employed to do."
Cabinet Office minister Liam Byrne denied Mr Wright's claims a culture had grown up around special advisers in which they got "dirty" with the complicit encouragement of ministers.
"I think special advisers do live within the spirit of the code," he told the committee.
He said Mr McBride was "an individual who had completely transgressed" the rules and had been punished for it.
He said the existence of special advisers helped preserve the impartiality of the civil service.