When the exit poll that foretold of Labour’s worst election defeat since 1987 was published, many in the party reacted with stunned incredulity. But Tom Watson, a self-described campaign veteran, was not one of them. “Having been around a while I knew that it was very bad news immediately,” the West Bromwich East MP tells me when we meet 11 days later. “I tried to believe Paddy Ashdown when he said ‘I’ll eat my hat’ but I know how large a sample [the polls] are.”

Watson, who served as Labour’s campaign co-ordinator from 2011 to 2013, says this feeling was informed by decades of experience. “I first started collecting numbers for the Labour Party when I was seven years old in the 1974 election. I stood on the steps of Walworth Road next to Neil Kinnock the day we lost the ‘87 election. I was working at Millbank when we won the ‘97 election. I’ve been there for the highs and the lows.”

At the age of 48, 14 years after entering parliament, Watson is standing for the deputy leadership of the party. “When I started trying to think about what we need to do at the next general election I thought ‘this needs a campaigner, we need to pick ourselves up, we need someone who’s going to mobilise the party’ ... Frankly, I looked around and thought that might be me. That’s why I’m doing it,” he says. Watson tells me that he does not intend to endorse a leadership candidate and that he could “work with all of them”.

With Andy Burnham the early frontrunner for the post, and Watson the favourite to win the deputy role, Labour could soon have an all-male team at the top. What does he say to those, such as the acting leader Harriet Harman, who argue that gender balance is essential? “Well, I think they’ve got plenty of options from what I see,” he replies. “If you want an all-women team you can go for it. I can’t change my gender but people have got a choice.” Referring to past occupants of the post, he tells me that he aims to combine “the calmness of Margaret Beckett” with “the energy of John Prescott”.

Watson, who visited 109 constituencies in the seven weeks before polling day, says he offers “an election-ready battleplan”, describing himself as “an experienced campaigner, someone who can unify different parts of the party and genuinely be creative in the way we build our next campaign.” He urges “big personalities” such as Jim Murphy and Len McCluskey to stop “slugging it out”, warning that such “seismic rows” are “not doing anyone any good”. But while Watson frames himself as a unifier, others argue that he is a divider. Some MPs have never forgiven him for his role in the ousting of Tony Blair as Labour leader. One told the Sunday Times he would support Watson because “I don’t want to find a horse’s head in my bed”.

“I don’t understand that characterisation of me,” Watson says when I reference his mafioso reputation. “I think I’m a tough campaigner and if I believe in something I’ve got a reputation for pursuing it and being relentless. But frankly, I think that’s what the party needs when it comes to the next general election.” He adds: “We need to really look at community organising again. Did that four million conversations strategy actually work or was it just a research exercise? ... I’m a very big supporter of the Arnie Graf model of community organising, it comes out of the Saul Alinsky school. Saul Alinsky uses that quote, power only knows two poles: it either goes to wealth or people. And the Tories have definitely got the wealth, we’re never going to have the wealth, or certainly not in the next five years, so we’ve got to reconnect with the people and we’ve got to rebuild our base.” He says that the case of Scotland, where Labour lost 40 of its 41 MPs, he says the party needs to be “as radical” as possible and consider all options, including an independent Scottish Labour Party.

Watson emphasises that he is keen to avoid “easy conclusions” before studying the result in greater detail but offers some early thoughts on Labour’s future policy direction. He calls on the party to “look at the worst and the best” of the free movement of labour, describing the open borders policy as “the biggest issue that undermines the authority and legitimacy of the European Union in the minds of voters”. Watson, a more heterodox figure than many assume, also urges Labour to adopt a sterner stance on defence. “The expansionist aims of Vladimir Putin are a big threat to European stability,” he warns, calling on the party to back the 2 per cent Nato spending target. “I think it’s inevitable that we will need a larger infantry and more naval capacity in years to come.”

The scale of Labour’s defeat led some to conclude that the conservative press maintains the power to swing elections. Watson, the scourge of Rupert Murdoch’s News Corp, concedes that “we do need better relations with the press”. But he warns: “The press need to conduct themselves in an ethical way, we saw some terrible transgressions of what is reasonable during the general election ... We need a Labour leader to adhere to the principles of Leveson and push for that. If they choose to editorialise on the back of that or conduct themselves in their news coverage as a reaction to that, there’s not a lot Labour can do, we’ve got to be true to what we believe in.”

Some MPs have suggested that the next leader should be placed on an explicit temporary contract and face dismissal if they fail to poll well enough. But Watson is quick to scotch this idea: “I’m not sure if that is very sensible, you undermine a leader from day one”. In another appeal to unity, he concludes: “We are going to have swing in around this leader, there will be one leader, one programme and it’s one shot, win or lose. There’ll be no room for messing around.”