Former News of the World reporter Mazher Mahmood commissioned a private investigator to stalk Tom Watson at a Labour Party conference, the MP alleged.Watson told the Leveson Inquiry that Mahmood – known as the ‘Fake Sheikh – hired Derek Webb to trail him in 2009, to establish whether he was having an affair.He said emails between Mahmood and news editors Ian Edmondson and James Mellor described information he says is untrue. The MP - who sat on the Culture, Media and Sport select committee examining phone hacking at the News of the World - claims News International had a vendetta against him after he spoke out against the company.Watson told the inquiry he had no evidence there was a “craven understanding” between politicians and senior executives at News International but has been encouraging colleagues to come forward with stories of alleged blackmail and intimidation by the company.Lord Justice Leveson told the MP it was clear he did not have an entirely "dispassionate" view on the issues he was considering, and asked if he could urge other MPs to speak out about blackmail and intimidation by any newspaper group, not just News International.Asked why it had take so long for politicians to “wake up” to hacking, Watson said some had “closed their minds” to the allegations.He said: “I think they closed their minds to the potential for a major scandal at one of their key outlets for their message, and I think the personal relations between politicians and people at the company were too fibrous and close so that they couldn’t divorce their objective thinking. And I think they were frightened.”Watson said Labour MP Martin Salter was subjected to several invasions of privacy after he opposed the Sarah’s Law campaign run in the News of the World, going on to say MPs feared ridicule or humiliation in the press in relation to their private lives or professional mistakes.He added: “There was a sense that there was a mystique about the News International stable, that they had unique access to Downing Street and for a minister that was important, and the way you were portrayed in the News International papers was important and they factored that into their thinking.”He said Gordon Brown called him – some time after the 2010 general election – to say Rupert Murdoch had phoned Tony Blair to “call him off”.Both Blair and Murdoch have denied this, but Watson said he remembered the conversation clearly.He told the inquiry: “I can tell you the exact position I was standing when I took the phone call because the idea that Rupert Murdoch would call Tony Blair or Gordon Brown to phone me is not the sort of thing a back bench MP would forget too easily.”The MP denied leaking information to the Guardian or former News of the World journalist Ian Kirby but admitted speaking to Guardian reporter Nick Davies, who broke the Milly Dowler phone hacking story last year.Rhodri Davies QC, acting for News International, said there was no evidence any members of the select committee other than Watson had been placed under surveillance by the News of the World.