Just 16% of electorate expect coalition between Tories and Lib Dems to last another three years, according to ICM poll

Only one voter in six believes the coalition will survive until the 2015 election, according to a Guardian/ICM poll that shows the proportion expecting a collapse within two years has nearly doubled in two weeks.

The findings follow the most testing episode for the government with the collapse of the agreement to reform the House of Lords. Nick Clegg accused the Conservatives of breaking the coalition contract by failing to support plans to introduce an elected Lords, and retaliated by withdrawing support for a redrawing of constituency boundaries, which would have benefited the Tories.

Any hopes that the Olympics would obscure the outbreak of hostilities within the government have been scotched by the poll, which found that only 16% of the electorate expected it to stay the course to the planned May 2015 election, down by half on the 33% who had said the same thing to ICM two weeks before. The proportion expecting the coalition to last until a few months shy of the election is also down, from 23% a fortnight ago to 19%.

Expectations of an early collapse have hardened – 43% think the coalition will collapse over the next couple of years, a near doubling from the 23% in late July. In addition some 11% (up from 7%) expect the partnership to break down even sooner, to give an overall majority of 54% who no longer believe the government will last into 2015.

The poll was conducted online, while the previous one was conducted by telephone, and some methodology effect cannot be ruled out, although it would be unlikely to fully explain such a dramatic shift.

The findings came after David Cameron and Clegg held a Downing Street dinner on Friday, reportedly aimed at establishing a rapprochement between their parties, and as both men prepare for a midterm policy review in October. It is designed to demonstrate collective momentum, but each is displaying an increasing determination to highlight distinctive policies. Clegg has asked his advisers to draw up an independent economic programme, in a move that could – if it results in a break from chancellor George Osborne's economic programme – unstick the glue that has kept the parties together.

Until recently, Lib Dem ministers had argued that the deficit reduction programme was essential to maintain credibility with the markets. But as the economy has sunk into a double-dip recession, they have hinted that they would like to see a slackening in the pace of the cuts.

The Treasury chief secretary, Danny Alexander, startled some observers by saying last week the verdict of the credit rating agencies was not the be-all and end-all, and at the weekend it emerged that he will move a motion at his party's conference next month criticising the Conservatives' failure to embrace green investment as a means of recovery.

Vince Cable, the business secretary, has for months pressed for the government to lend its balance sheet to housing associations to launch an ambitious programme of building social homes. That has not led to direct conflict with the Treasury, but his wider demands for significant capital spending to stimulate demand could lead to tensions, as could plans he has been floating for using the wholesale nationalisation of RBS to forcibly increase bank lending.

The growing public belief that the coalition is going to collapse will unnerve Cameron, who is acutely aware that voters are not attracted to warring parties, even as he faces pressure for a more distinctly Conservative message from restive MPs. Clegg is also sensitive to the competing needs of presenting a united front while demonstrating that the Lib Dems have not abandoned their core beliefs in the pursuit of power.

Two polls published in other newspapers yesterday suggested the Olympics had done little to shift opinion. YouGov, for the Sunday Times, put Labour on 42%, the Conservatives on 34% and the Lib Dems and Ukip on 8% each. Labour's strength is unchanged since the last lot of fieldwork the same company did before the opening ceremony, and – although the Conservatives are up one point and the Lib Dems down one since that benchmark – such small changes are statistically insignificant.

Meanwhile ICM's so-called "Wisdom of Crowds" poll for the Sunday Telegraph, which asks respondents not whom they will vote for, but how they expect support to be split at the next election, produced figures of 38% for Labour, 31% for the Tories and 17% for the Lib Dems. These results are identical to those produced by the same method last month.

ICM Research interviewed a sample of 2,021 adults aged 18-plus online on 8 to 9 August 2012. Interviews were conducted across the country and the results have been weighted to the profile of all adults. ICM is a member of the British Polling Council and abides by its rules.