A ComRes poll for Wednesday's Independent newspaper showed 66 per cent of Britons are against changing the way members of parliament are elected, against 34 per cent who want to move to the Alternative Vote (AV) system.
The referendum, to be held on Thursday along with local elections, has exposed rifts in the Conservative-led government.
The Conservatives back the status quo, while their Liberal Democrat allies back a move to an AV system which favours smaller parties.
Tensions over the issue spilled over into a cabinet meeting on Tuesday when Lib Dem Energy Secretary Chris Huhne confronted Prime Minister David Cameron over campaign leaflets that criticised Lib Dem leader Nick Clegg.
Coalition governments are rare in British politics -- this is the first since World War Two. The first-past-the-post voting system has marginalised the Liberal Democrats, creating two-party election battles that normally end with single party -- Conservative or Labour -- majority governments.
Voting reform was one of the biggest stumbling blocks in creating the coalition after an inconclusive election in May last year. The Lib Dems ultimately want a system of proportional representation but accepted AV as a compromise.
The harmony with which the left-leaning Lib Dems and the centre-right Conservatives had pressed ahead with a deficit-cutting agenda in their first year had surprised many.
Markets want a stable government to see through a five-year plan to tame the budget deficit by 2015.
The question now is whether the coalition partners can get back to business as usual after the referendum and local elections in which voters are expected to desert the Lib Dems.
Clegg, the deputy prime minister, said on Tuesday that the distinct identities of the two parties would begin to emerge more clearly after a first year marked by coalition unity.
Lib Dem activists in the western English city of Bristol, a party stronghold, told Reuters they did not believe it was time to quit the alliance.
"If we lose (the referendum) it will be difficult, but that is no reason to ditch the coalition. Ultimately the work of the coalition and getting the country right is more important," said Lib Dem councillor Simon Cook.
The Lib Dems risk losing control of local power bases like the cities of Bristol, Newcastle and Sheffield on Thursday as voters punish them for policy U-turns in government, notably signing up to higher student tuition fees.