The former prime minister was in Elderslie, birth place of the Scottish warrior who inspired Mel Gibson’s blockbuster movie Braveheart, to give his backing to Labour candidate Douglas Alexander who has a fight on his hands to hold on to his Paisley and Renfrewshire South seat.

Mr Brown told a gathering of Scottish Labour supporters that Mr Alexander could achieve more in a 50 minute cabinet meeting than 50 SNP MPs could achieve in five years.

Although Mr Brown never once mentioned Mhairi Black’s name – or William Wallace’s for that matter – it was clear his jibe was aimed at the 20-year-old Glasgow University student and SNP candidate being tipped to put the shadow foreign secretary to the sword on May 7.

Speaking to a captive audience at Elderslie Village Hall, he said: “It’s a privilege to be in Paisley and Renfrewshire South constituency to speak for a local man who has served brilliantly as your MP.

“And I tell you from my experience as prime minister that Douglas Alexander will do more to bring positive change in a 50 minute cabinet meeting as a Labour minister than even as many as 50 SNP MPs could achieve in five years of protest outside of government.” Ms Black meanwhile, took to the streets of Paisley over the weekend and in an online interview she said Mr Alexander should take his fair share of responsibility for Labour’s “failure to deliver” for ordinary people.

She said: “He’s been consistently high up in the Labour Party which means he’s one of the very people who need to be held accountable for the fact that Labour has not delivered for ordinary people and certainly not for Scotland in all the time they have been our representatives.” Mr Brown’s arrival in Elderslie came on the same day it emerged that the depute provost of Renfrewshire Council, John Caldwell, had been reported to police amid claims he urinated in a voter’s garden, just a few minutes’ walk away from the village hall where Mr Brown delivered his speech.

Former Park Mains High School teacher Brian Wright called the police after he claimed to have seen the Labour councillor relieving himself in a bin shelter during a door-to-door canvassing session in Elderslie on behalf of Mr Alexander, who is one of Mr Wright’s former pupils.

The 59-year-old, who is demanding an apology, said: “I was having a cup of tea and reading a book when I saw a man walking into the bin shelter.

“I didn’t think it was suspicious at the time and just assumed he was going to put some rubbish in the bin.

“But he seemed to be in there for rather a long time and after a while I began to wonder.

“I could see him shuffling around inside then he walked out with a satisfied look on his face.

“I ran outside and looked in the bin shelter where there was a huge puddle.” The unsavoury allegation failed to rain on Mr Brown’s parade has he fired a broadside at Ms Black and highlighted Mr Alexander’s political credentials.

He said: “I think the issue is that someone who is clear that they want a second referendum immediately is someone who I think the people of Paisley and Renfrewshire South will not want to elect as their MP.

“It’s what she says about twisting people’s arms and delivering a second referendum that make me realise that she’s not going down there, or wanting to go down there, to talk about the Royal Alexandra Hospital and the needs it has, or about the jobs needs that Paisley always has as a result of the changing economic environment or about the housing needs of Paisley.

“I mean, these must be the most important issues. Paisley and Renfrewshire needs more houses, more jobs, it needs better health care services. You’ve got a hospital using special measures, a shortage of nurses and you’ve got a Labour promise that 1,000 nurses and 500 doctors are going to be in to the health service as soon as we can achieve that.” Mr Brown said the SNP was “obsessed” about a second referendum and suggested people in Scotland didn’t want more “divisiveness and acrimony” and, he insisted, Mr Alexander was in a better position to tackle local issues as part of a Labour government.

He went on to dismiss the suggestion that voters are drawn to a new face like Ms Black because she is seen by some as an antidote to a failing Westminster.

He said: “But the change that people actually want is a better health service, more jobs, and they want more houses and they want a government that actually cares enough to end austerity and cares enough to end the bedroom tax and to end the need for food banks. I think when you’re looking at this election it’s about what the parties will do and the only way to ensure a better health service, better job prospects of young people, deliver the housing that needs improved is having a Labour government.” The outcome is far from certain, of course, and much has been made of the recent Lord Ashcroft poll which has Ms Black eleven points ahead of her Labour rival.

But Mr Brown urged people to stick with a man he says has the credentials to make a real impact in an Ed Miliband government.

He said: “A few hours of Douglas Alexander in a Labour cabinet, deciding to end the bedroom tax and raise the minimum wage is worth far more to the people of Paisley and Renfrewshire than five years of simply protest at Westminster when you’ve got a Conservative government.” He added: “Douglas is the local man with huge experience who has not only served this constituency with distinction over the past few years but he was also brought up here, went to school here, knows the areas and has a tremendous reach into the communities. I think his local record is exemplary but also he will be the man around the cabinet table that you can genuinely say every week is speaking up for Paisley and Renfrewshire.” Ms Black was also making her presence felt in Paisley over the weekend and an interview she gave to a political blogger has already attracted thousands of views online.

In the You Tube video she said: “See to be honest, I don’t think it’s about me and equally I don’t think it’s about his [Douglas Alexander] personality either. People are so politically educated now that they want arguments, they want quality in their arguments, and they want decency and honesty and passion in their politics. That’s why I think people are turning to the SNP.

“The Labour Party that exists now is not the Labour Party that my Granda voted for, it’s not even the Labour Party that my dad voted for. They’ve forgotten all their principles, they’ve abandoned all the people they are supposed to represent.” The SNP’s John Swinney, deputy first minister, suggested it was Mr Brown who was re-fighting the referendum, not the SNP who, he said, were focused on giving Labour “backbone” at Westminster.

He said: “Brown’s speech simply reminds people once again of how Labour stood shoulder-to-shoulder with the Tories for two-and-a-half years to talk Scotland down.

“The question Labour’s current leadership have repeatedly failed to answer is, if there are more anti-Tory MPs — between the SNP and Labour — than there are Tory MPs, will they work with us to lock the Tories out and to deliver better policies for people, not just on Scotland but across the rest of the UK?

“A strong team of SNP MPs can give Labour the backbone to oppose further cuts and pursue a progressive alternative to austerity.”