Ed Miliband predicts that the Conservatives will be thrown out of office by Labour after one term in Downing Street, as David Cameron faces fresh allegations over failing to declare numerous secret meetings with rich Tory donors in the "cash for influence" scandal.

After a week that has seen the Tories battered by rows over party financing, embarrassed by a row over VAT on takeaway food and accused of stoking a crisis at the petrol pumps for political gain, the prime minister was accused of a "cover-up" by the Sunday Times.

The newspaper claimed that Peter Cruddas, the disgraced former Tory treasurer, mixed with David Cameron and large donors at more than a dozen private events, including bankrolling a dinner at Chequers, despite the party's attempts to disown him as a minor player. Cruddas's name was absent from a list published by Downing Street to show that the party was being transparent about Cameron's meetings with wealthy businessmen, the newspaper added. In new video footage, Cruddas also boasts that he had secured a donation of £1m only a fortnight before his resignation, despite Tory claims that he had never brought in a big cheque.

A Conservative spokesman said last night: "Of course, politicians meet donors as they do thousands of individuals every day. But the key question is whether these meetings influence policy and they categorically do not."

In an interview with the Observer, Miliband said Cameron's entire political project has been fatally undermined by rows over donations, tax cuts for the rich and the petrol crisis. He also accepted that Thursday's byelection defeat in Bradford West, where Labour lost a previously safe seat to the maverick anti-war candidate George Galloway, had been a "deep disappointment" for which he accepted responsibility.

But he insisted the "tumultuous events" of the past week had, unlike the byelection, fundamentally changed the political game.

"I think it is going to be remembered for the end of the Cameron project," Miliband said. "Thursday night was a very bad result [for Labour] but there is a big picture about where politics is and I think people will look back on the last few weeks and say, 'that was when the Cameron project hit the buffers and this was when Labour had their chance'."

Striking a more optimistic note than he has done in the past 18 months about Labour's chances in 2015, he said that while his party had much to do, and he was far from complacent, he was now confident the Tory-Liberal Democrat coalition would be a one-term government. "Opposition is a long and difficult haul," he said. "It is going to be a one-term haul, I am confident about that."

Meanwhile, polls revealed voters believe the government has lost touch with ordinary people. An Independent on Sunday/Sunday Mirror ComRes poll found 72% said the coalition was "out of touch with ordinary people". Four out of five of those questioned said that ministers had caused an unnecessary panic over the threat of a strike by tanker drivers.

After a dreadful few days, the government was offered some relief early on Friday morning when Galloway, the Respect party candidate, stunned the political establishment as he stormed home with a 10,000 majority in a Labour stronghold. Miliband said the lessons from an unusual seat, with a large Muslim vote, and huge numbers of last-minute switch voters, had to be learned. "Right up to the time the polls closed, we weren't expecting to lose," he said.

With the party leaders turning their attentions to the local elections in May, Miliband says he will campaign on a theme of "fairness in tough times", focusing on fair wages, the NHS and crime.

Cameron will also conduct a national tour during which he will try to end 10 days of attacks on George Osborne's budget for favouring the rich, as well as criticism over alleged secret deals with multimillionaire donors.

The Tories are also at the centre of new claims that they deliberately stirred up public anxiety over fuel supplies to deflect attention from their own problems. In an article in the Daily Telegraph, the paper's ex-editor and columnist Charles Moore, who is a friend of Cameron and well connected, wrote that the "private message" to local Conservatives described the growing anxiety as "our Thatcher moment", where Tories could turn the situation to their advantage by stockpiling petrol, as Thatcher stockpiled coal, thus defeating any strike and putting the blame on Labour.On hearing Moore's account, Unite leader Len McCluskey said evidence that the run on petrol was the result of political manipulation could scupper the prospect of peace talks at Acas.

"We call on the government to come clean on its whole approach to this dispute … Over the last few days its every move has been designed to whip up unnecessary tension at the expense of the public. Ministers knew all along that a strike could not possibly be less than seven days away even were it to be called – that is the law. Yet they panicked the nation all the way to the petrol pumps because they imagined it would boost them in the polls."

Maria Eagle, Labour shadow transport secretary, said: "These allegations are outrageous. People will be angry that David Cameron has inconvenienced millions in an attempt to create his own 'Thatcher moment'. The prime minister should apologise to the country for the chaos his government has created."

The Tories denied such instructions had been issued.