THEY used to call Tom Watson a paranoid conspiracy theorist, but they're not laughing now.

Mr Watson is the Labour MP who, along with fellow MP Chris Bryant, journalist Nick Davies, lawyers Charlotte Harris and Mark Davies, and several whistleblowers, has done much to expose the phone-hacking scandal. Yesterday, digesting the latest emails to surface at the Leveson inquiry, he said Culture Secretary Jeremy Hunt had to resign; even the most cynical Leveson-watchers, he added, would be shocked by the extent of the links between the Government and News Corp.

Mr Watson's engrossing new book, Dial M for Murdoch: News Corporation and the Corruption of Britain (in which he and co-author Martin Hickman accuse Rupert Murdoch of running a "shadow state") examines the scandal's complicated background while throwing light on the personal cost it exacted. In late 2010, he was not only unable to get much traction in his investigations but was struggling personally. His marriage, strained by the Damian McBride affair (McBride was the Labour special adviser who resigned over rogue emails) and his preoccupation with phone-hacking, had collapsed, and he was leading an itinerant life – in London as an MP, West Bromwich for his constituents, Yorkshire for his children. Over Christmas, he would rise early and, if he was in Yorkshire, tramp the hills, ringing his best friends for up to an hour with his latest ideas for the investigation.

He had already begun to worry about his security. He was, as he acknowledges, in a state of constant paranoia. Many people urged him to back off, but he persisted. He has been vindicated, to an extent he could scarcely have imagined a year ago.

We could do with more MPs such as Tom Watson.