Under-fire Watson hits back

And no wonder. For at his own expense, the West Bromwich East MP has consulted London's famous – and hugely pricey – libel lawyers, Carter-Ruck.

The MP, spending the Easter break with his wife Siobhan and their two children, said: "For the first time in my life I have had to involve lawyers with national newspapers.

"But I had no choice. I have been seriously defamed in a national newspaper. All you have in politics is your reputation."

Speaking of the Smeargate scandal which led to the sacking of Gordon Brown's spin-doctor Damian McBride, Mr Watson said: "I absolutely should not be involved in any of these stories because I have nothing to do with it."

But as the Government's expert on cyberspace and blogging, and as Cabinet Office minister at the heart of Downing Street, did he know nothing of McBride's scandalous website Red Rag?

"I had absolutely no knowledge whatsoever until we found out about it on Friday afternoon."

But was he not both physically and politically close to McBride in the No 10 office?

"I didn't share an office. I didn't sit by him. That is another lie."

The Times today ran a two-page spread on "Gordon's Reservoir Dogs". Tom Watson was depicted as one of six black-suited heavies who do Brown's dirty work. The others were Education Secretary Ed Balls, Chief Whip Nick Brown, Assistant Whip and Dudley North MP Ian Austin, former Labour spin-doctor Charlie Whelan and McBride himself.

Tom Watson has long enjoyed being part of Gordon Brown's laddish inner circle. But he is clearly furious at being associated with McBride's plan to "destabilise" the Tories by spreading rumours of adultery and embarrassing diseases in cyberspace.

In its statement Carter-Ruck says: "We have today written to the editors of the Mail on Sunday and the Daily Mail to complain about the publication of the false allegation that our client had knowledge of, and participated in, Mr McBride's actions." One thing is certain. Tom Watson has never had a week like this one. Until Easter weekend he was best known as the plump and generally jovial master of the blogosphere.

He was Parliament's first blogger and his daily blog (web log) shows how anyone in public life can use the internet to keep in touch with constituents and – best of all – present an image of themselves that the traditional media of newspapers, television and radio never would.

Since the Smeargate scandal broke, Mr Watson's daily blog has fallen silent. Sharp- eyed visitors to his website might spot a section call "My Tiny Plot," which turns out to be nothing more sinister than a section on growing vegetables.

But an echo of today's problems can be found in the MP's list of "25 books I've read in the last two years that have influenced, interested or amused."

Number 15 is Mudslingers: The Twenty-five Dirtiest Political Campaigns of All Time by Kerwin Swint.

Commenting on the book, Tom Watson writes: "These campaigns make Liberal Democrats look like angels." But today it is his beloved Labour Party which is looking less than angelic.

In a speech last year Mr Watson reflected on his decision to set up his political blog: "At the time it was seen as a radical act. People could not believe that I had opened myself up to such scrutiny and occasional daily abuse. I sometimes still wonder about that bit myself."

Today, Tom Watson must be reflecting on the furore caused by a leaked email. Cyberspace offers enormous political influence. But it can also bite you when you least expect it.