Tom Watson is a little bleary but otherwise in good spirits. Exposing the dark heart of the world's most powerful news corporations is physically demanding, black coffee-fuelled, exhilarating work; he doesn't always get eight hours sleep. In fact, for the past three weeks, the 44-year-old scourge of Rupert Murdoch has averaged three hours a night as he gives TV interviews, writes letters to Scotland Yard, asks Commons questions and generally causes havoc to Mr Murdoch's hopes of continuing in business in Britain.

His two-year campaign to uncover the scale of wrongdoing at Mr Murdoch's News International (NI) dramatically burst to life three weeks ago with the disclosure that its best-selling paper, the News of the World, had hacked into the mobile phone of Milly Dowler.

The ensuing "firestorm" (David Cameron's words) forced the Prime Minister to open a public inquiry and Rupert Murdoch to abandon the tabloid and, eventually, the redtop he had been hoping to keep, NI's chief executive Rebekah Brooks.

At every stage Watson has popped up on TV, newspaper front pages and Twitter undermining the PR counter-offensive from Britain's biggest newspaper group. He has also kept up the pressure in Parliament, where last week, as the resident phone-hacking expert on the Culture, Media and Sport Select Committee, he came face to face with the Murdoch clan: Rupert and James, and their former British chief, Ms Brooks. Commentators judged Watson's questions to have been the most incisive and he repeatedly refused to let Murdoch Junior jump in for his father.

As he waits for his lunch at a Mexican restaurant in Fulham, where The Independent tracked him down, Watson pauses as he works out how to sum up the last few extraordinary weeks. "It has seemed like surfing a giant wave for two weeks solid," he says. "I've not been able to look down, nor take it all in."

His newfound fame has won him the admiration of assorted showbusiness stars. The strangest experience, he says, was George Michael calling him his hero, and he also had his hand shaken effusively last week by the comedian (and Sky TV quiz host) David Walliams, who stopped him on London's South Bank.

Since joining the DCMS committee's inquiry into press standards in 2009, he has been preoccupied with the misdeeds of Britain's biggest newspaper group – some would say obsessed. He starts his day thinking about how to tackle the fast-moving story and goes to sleep thinking about the next line of attack. Despite the tumultuous events of the past weeks, he believes the "phone-hacking scandal" still has a long way to go. "I don't think we're half way through it," he says, munching through the starter.

"We're a lot closer to the people at the core of the organisation who really run News International; we're a lot closer to finding out who knew what. But as to the actual number of victims and types of criminal invasions of privacy, I don't think we're anywhere near to getting that story out yet."

The revelation about Milly Dowler almost instantly shattered the Murdochs' political power. Labour and Conservative politicians who had been paying their respects to the family at their summer party in London two weeks earlier were suddenly desperate to distance themselves from their empire.

Ed Miliband made the running by demanding a public inquiry and the head of Ms Brooks, both of which duly arrived. By contrast, Mr Cameron was left responding to events, his position made all the more difficult by his initial defence of his former communications director Andy Coulson, the ex-NOTW editor, who was arrested over alleged police corruption.

Watson, Labour MP for West Bromwich East since 2001 and a friend of Gordon Brown, is pleased at his leader's stance. "I'm really very proud of Ed Miliband," he says. "I hope my colleagues in the Parliamentary Labour Party, the Labour Party and the country are in no doubt that he is the only candidate at last year's leadership election that would have called for Rebekah Brooks to go at PMQs, and we should all be proud that that we elected him.

"He probably made one of the biggest political calls of his life – and he made the right call."

As to Mr Cameron, Watson is bemused why he seems to be "constantly behind the curve on this".

"Don't get me wrong," he says. "I admire the fact that he's now agreed to a judge-led inquiry and a full investigation can now take place and I don't discount that. But he has lost his usual surefootnedness on this issue and he looks a little evasive."

Within Parliament, MPs from all parties have been personally warm, he says. "It's heartening. Colleagues from both sides of the House have been very supportive. I think they regard the matter as a stain on the character of the country and they understand that collectively we've got to put that right.

"Some of them used to rib me a year ago when they thought I was being mildly obsessional in my pursuit of the facts of this case and, in an embarrassed way, have apologised for making fun of me, so there have been some amusing moments as well." He continues: "We've had lots of letters phone calls and emails in the office and people have stopped me in the street and said, 'Well done'."

Before he become known for his role in covering the scandal, Watson was a leader of the "Curry House plot" to unseat Tony Blair in 2006, for whom he was a defence minister. Gordon Brown made him a minister in 2008, putting him in charge of government modernisation at the Cabinet Office.

He has an interest in technology and was one of the first MPs to blog and use Twitter. While many newspapers were not reporting the scandal, social media was "key", he recalls, adding that the papers that did investigate were "The Independent, the Independent on Sunday, the Guardian and FT".

"The other papers were not reporting the story, so it was social media that kept the issue alive and many thousands of people on social media have been concerned that a cover up has taken place.

"I think the story might not have come about had not people using social media expressed their outrage. Certainly without Facebook or Twitter a consumer boycott of the advertisers of the News of the World would not have been organised so quickly."

Watson adds: "Even more embarrassing the editor of a website called Labour List is running a campaign for me to carry the Olympic torch which would" – the rotund MP laughs – "actually be the ugliest image in sporting history."

Life in brief

1992 President of the NUS and chair of the National Organisation of Labour Students while at the University of Hull.

1993 National Development Officer for Youth for Labour Party.

2001 Elected MP for West Bromwich East.

2006 Resigned from Ministry of Defence after signing letter calling on Tony Blair to stand down. Told BBC News that Rebekah Brooks said she "would never forgive [him] for what I'd done to her Tony".

2009 Awarded damages by The Mail on Sunday and The Sun for carrying stories that claimed he knew about smear emails sent by Labour adviser Damian McBride.