A leading Liberal Democrat candidate has warned that party activists in Kent would "struggle" to accept any deal with the Conservatives that did not include a commitment to change the voting system.

Peter Carroll, who stood in Maidstone and the Weald and cut the Conservative majority to just under 6,000, said rank and file party members would not be happy if Nick Clegg failed to extract a pledge over a referendum on changing the way MPs were elected.

His comments come amid reports that many activists and ordinary party members from both sides are uneasy about a formal coalition government.

The two parties are continuing talks today about a formal pact. Under party rules, Mr Clegg has to get the endorsement of party members for any deal.

Mr Carroll said: "I have spent all my life in Kent fighting the Conservatives because I think there are big differences between us. I totally accept that the national interest has to come first but I would really struggle with anything less than a [pledge] for a referendum on proportional representation. It is putting the country first because we have a system at the moment where the problem is that we end up with governments who feel they can do what they like. I know many, many people in Kent in the party who would not be happy if there is no commitment to PR. Without it, they will struggle to accept any deal."

He said the reason why the Conservatives had reasserted their grip on the county was because the first-past-the-post system meant many people felt voting for the Lib Dems was a waste.

"Until the voting system is changed, that attitude will remain," he said.

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