London: British Prime Minister David Cameron and his deputy expressed confidence that the coalition government would survive a bitter battle over changing the voting system.

Voters will decide in a historic referendum on Thursday whether to change the system of first past the post, where the candidate with the most votes wins, or replace it with the alternative vote (AV), a system of preference votes.

Cameron has been vigorously campaigning to keep the old system, backed by his Conservative party, while Deputy Prime Minister Nick Clegg, the leader of the Liberal Democrats, is desperately trying to convince the public of the need to change.

After early signs of support for the "yes" camp, polls now indicate a "no" vote is likely -- a BPIX survey for the Mail on Sunday newspaper found 51 percent opposed the reform and just 33 percent backed it.

But the vehemence with which the campaign has been conducted has surprised many, and sparked fears for the future of the coalition which marks its first year in power this month.

Lib Dem Minister Chris Huhne accused his rivals of "completely trashing us and Nick Clegg's leadership" in comments published on the Guardian's website Sunday and Clegg himself has accused his opponents of "lies, misinformation and deceit".

The Tories meanwhile have told the Lib Dems to stop "whingeing" and Foreign Secretary William Hague suggested AV was a "loser's charter".

"We always knew that this would be a moment of difficulty for the coalition because we always knew that Conservatives and Liberal Democrats would be on opposing sides in this campaign," Cameron said.