Disgruntled binman shouts at Nicola Sturgeon during press briefing

Ms Sturgeon was ambushed by Charlie Docherty when she stopped to talk to him ahead of a press briefing on Calton Hill in Edinburgh.

Mr Docherty, 53, told her "you need to do something" about the dispute between refuse workers and Edinburgh City Council over terms and conditions and pay.

He voiced fears that a renegotiation of his contract might leave him better off but would leave colleagues poorer.

Mr Docherty, who was sat at the wheel of his lorry, said: "She just stood there and said she doesn't know what I'm talking about, but they're the Government of this country."

He revealed he would be voting Labour on May 6. Mr Docherty, who has been a binman for 25 years, said: "I voted for the SNP last time round and the time before that and the time before that, and I believed them."

Ms Sturgeon told him: "We're here today highlighting the high costs of fuel, we don't think people at the bottom end should be paying the costs of the economic downturn.

"We don't think people on lower incomes should have their wages cut."

Ms Sturgeon and Justice Secretary Kenny MacAskill arrived on Calton Hill in a hackney cab emblazoned with "Vote SNP".

They were accompanied by SNP candidates George Kerevan, for Edinburgh East, and Calum Cashley, for Edinburgh North and Leith.

Ms Sturgeon said the fair fuel price regulator, which forms part of the party's manifesto, is "a very simple idea".

She said: "Fuel prices are too high and that's hitting family budgets, small businesses and road hauliers.

"If the price of oil goes up, we would bring the fuel duty down. I think people would want to see fuel prices go below 1 per litre."

Ms Sturgeon acknowledged that fuel prices are a reserved issue decided by the UK Parliament. She said: "It's something the SNP MPs and champions will argue for."

Referring to Mr Docherty, she added: "This is a dispute between Edinburgh City Council and the binmen, it has to be resolved between them."

She said the SNP was the only party to lobby against public sector cuts and was in favour of pay freezes for those at the top end of the scale in order to protect lower-paid workers.

Ms Sturgeon also said tonight's leaders' debate on foreign policy, which is being broadcast live by Sky from Bristol, would show there was little difference between Labour, the Conservatives and the Liberal Democrats.

She said: "Our exclusion (from the debate) is entirely undemocratic for voters in Scotland. In this election, people are looking for an alternative to the discredited Westminster politicians."

Ms Sturgeon also indicated she thought "there was every possibility" this might be the last General Election to use the first-past-the-post voting system.