The first thing that strikes you about Mark Serwotka is how mild-mannered and reasonable he seems. Born in Cardiff in 1963 and raised in the valleys after being adopted from a Catholic orphanage, he speaks with a soft Welsh accent and comes across as a calm and intelligent man. Yet critics have described the leader of the Public and Commercial Services Union (PCS) as the "most ideologically driven and politically asinine of the union top brass" (Independent) and an "unreconstructed Trotskyite" (Sunday Times). At a recent meeting of union leaders, Brendan Barber, general secretary of the Trades Union Congress (TUC), called him a "fundamentalist".

On 15 June, Serwotka's union voted to go on strike over proposed reforms to public-sector pensions, joining teachers' unions including the National Union of Teachers, the Association of Teachers and Lecturers and the University and College Union, which had agreed on a mass walkout at the end of the month. With up to 750,000 teachers, lecturers, civil servants and public-sector workers ready to take co-ordinated action, 30 June could be the biggest day of strikes in years.

So is Serwotka the new Arthur Scargill, intent on waging war with the government? He describes himself as a "radical socialist". Is he a Marxist? He hesitates. "Am I a Marxist? Hmm." Another pause. "I was in a Trotskyist organisation when I was younger - the Socialist Organiser - but only briefly. I was influenced by Marxism but I've never been doctrinaire."

In recent years, he has "flirted" with various left-wing parties, including George Galloway's Respect, and he voted for the Green Party in the last general election. But in the local elections this year, he spoiled his ballot paper. "I've never subscribed to the lesser-evil-ism of modern politics," he explains. "Growing up in Wales, it was Labour, Labour, Labour. But [since] its move rightwards and embrace of the markets, Labour doesn't speak for me."

Serwotka dropped out of school at the age of 16 and became a civil service benefits clerk. He asked to join the union on his first day. Within a month, he was on the branch committee. "I have always believed that unions are very important," he says. "I guess it's something rooted in the way I was brought up."

He was elected general secretary of PCS in November 2000, defeating the Blairite incumbent Barry Reamsbottom (who initially refused to accept the result). One of Serwotka's campaign pledges was that he would refuse to take a full wage, yet his salary in 2009 was £86,244. "The union's executive voted not to allow me to have a lower rate of pay, as it affects collective bargaining," Serwotka says, before reminding me that, since 2001, he has donated £80,000 out of his wages to the union's hardship fund. "I don't think any other union leader has given that amount of money," he says. "But I admit that I am incredibly well recompensed compared to the people I represent."

Those 300,000 people who make up the country's fifth-largest trade union work in a range of government departments and include benefits officers, tax inspectors and court clerks. Serwotka describes the government's plans to force his members to "work longer, pay more and get less" as "naked deficit reduction" and a "tax on public-sector workers".

He makes it clear that the PCS ballot was about jobs and pay as well as pensions. His union claims that 100,000 jobs are at risk. "The pensions issue," he says, "was just the vehicle that allowed for legal, co-ordinated strikes with the teachers' unions. If we are defeated on pensions, it makes it a lot easier to cut the jobs and services but if we can fight back, then the ability for that resistance to broaden out shouldn't be underestimated."

Bubble boys

Serwotka is confident and well informed. When I ask about rising public-sector pension costs, he points to page 22 of the March 2011 report by the former Labour cabinet minister John Hutton (which forms the basis of the coalition's plans on pensions) and states that payments will "fall gradually to around 1.4 per cent of gross domestic product in 2059-2060, after peaking at 1.9 per cent of GDP in 2010-2011".

What about the accusation that the strike has limited support inside his union? The turnout in the ballot was only 32 per cent, so the 61 per cent who voted in favour represents just one in five members. "I wish the turnout was higher, but if the coalition wanted a higher turnout, they'd make it easier to vote, not harder. Why can't we have internet voting, telephone voting and secret balloting in the workplace under supervised conditions?"

As for Hutton's argument that we have to "face up to the financial consequences" of living longer, Serwotka cites Work, Stress and Health: the Whitehall II Study, published by the Cabinet Office in 2004, which shows how workers in the lowest civil service employment grades were much more likely to die prematurely than those in the highest grades. "How can you ask people to work for 50 years," he says, "if, as in my case, they left school at 16?"

He says that he is prepared to accept Hutton's recommendation for a public service pension scheme based on career-average earnings rather than final salaries - his union agreed to career averaging for new entrants in 2005 - but there is a condition: "We're up for negotiating on career averaging if it is based on the same costs and not based on driving the costs down."

Does he have a bottom line? "No one should have to pay any extra money unless their pension scheme valuation deems it necessary; there should be no central increase in the pension age and the government should be prepared to negotiate the inflation-indexing of pensions." But Serwotka doesn't believe that coalition ministers are interested in negotiations. He points to a speech made by the Chief Secretary to the Treasury, Danny Alexander, on 17 June, which announced detailed plans to increase pension contributions - and the working age - for millions of public-sector workers, all without the agreement of unions.

Didn't the PCS pre-empt the outcome of negotiations by calling a strike two days before Alexander's intervention? Serwotka shakes his head. "They have already changed pensions from RPI [Retail Prices Index] to CPI [Consumer Prices Index], reducing the value by 15 per cent. They have already announced contribution increases - in the Spending Review - so we're striking because of the things that they've already done and are already happening."

So, what happens to negotiations? He insists that, without strikes, the chances of the unions' negotiations with the government being successful are "nil".

“I always take the view in negotiations that if they don't see anyone putting pressure on them, there's no pressure to concede," he says. "I think the 30 June strike action will show that people are not prepared to accept the changes and one of two things will happen: ministers will decide, 'We have to see them off,' and harden their position, or they'll say, 'All right, then, we're going to be a bit more meaningful about our discussions.'"

Serwotka predicts a bleak future for industrial relations in the UK. "After 30 June, we will be having more strikes, department by department, against specific job cuts. In essence, we see 30 June as a political event - about mass mobilisation to put pressure on the government. The strikes in departments will be about making those departments and ministers feel the consequences of cutting jobs."

He views the coalition government as right-wing, cynical and cruel. "They've used the economic woes as cover to do things that some of them have been dreaming about for years. It is class warfare; it is about shrinking the state, shrinking welfare and taking on the unions."

Does he believe that ministers are indifferent to the fate of his members and that of other public-sector workers? "I don't think they give a shit," he says. "People who have lived in a bubble of privilege all their lives have no concept of what ordinary life is like." What about the Labour Party? Unlike the four big unions - Unite, Unison, GMB and the Communication Workers Union - PCS is not affiliated with Labour. "I think Ed Balls is becoming more combative," Serwotka says. "He has moved leftwards since he left government." He seems less keen, however, on the Labour leader. "For me, Ed Miliband has been disappointing. He's not confident or robust enough."

Fight club

Is Serwotka walking into a Tory trap, giving the Chancellor, George Osborne, the confrontation that he wants that will divert attention from a failing economy (as Balls, among others, has suggested)? He shrugs. "I think it's very easy to talk yourself out of doing anything. Not doing anything means defeat and it invites more aggression." He admits that his militant approach has put most of his fellow union leaders "on the spot" - especially after the TUC march and rally on 26 March, which "was brilliant", but "didn't save a single job or service". Many activists in other unions, he claims, are asking: "Why aren't we doing any of this?"

Serwotka prefers not to use the language of "general strikes" or to hark back to the miners' strike as Unison's general secretary, Dave Prentis, did in a newspaper interview on 18 June. Nonetheless, he predicts that Britain is on course for the "biggest strikes, in terms of numbers, in decades".
“The only reason I don't use the phrase 'general strike'," he says, "is that I think what you say should have a clear resonance and should be deliverable. And it is deliverable to have co-ordinated strikes involving millions."

He believes that these mass strikes will be ongoing in a year's time - "I think they will grow incrementally" - and says it is "possible" that they will continue throughout this parliament. "The difference between us and the miners is that, in an all-out strike, there was a demonstrable point where you won or lost, but what we're doing is rolling, and much more political. This is not about bringing employers to their knees but about forcing the government to back down on cuts."

Yet is he in danger of meeting the same fate as Scargill, who picked a fight with a Conservative-led government that he couldn't win? "I admire a lot of what Scargill did," Serwotka says. "I don't share his politics but I admire the bravery of the National Union of Mineworkers leadership and I have no doubt that they were right to do what they did."

But they lost, I point out. "I don't take the view that we can't win," he says.

He ends with a very personal and combative message for the government - and, perhaps, for his fellow union leaders, too. "My father once said to me: 'If you fight in life, you're not guaranteed to win. But if you never fight, you lose every time.'"

Mehdi Hasan is senior editor (politics) of the NS