The Tories have called on the government to scrap all postal ballots in the forthcoming regional assembly referendums.

Speaking ahead of an opposition day debate, Conservative constitutional affairs spokesman Alan Duncan warned that the "integrity of the ballot box" must be maintained.

His criticism comes amid claims that all-postal ballots in the recent European elections led to higher fraud levels.

Duncan also called on the government to back away before attempting to use universal all-postal voting in any EU constitution referendum.

"Greater participation in elections should be a sign of a healthy democracy – but increased turnout should not come at such a high cost," he said.

"The government's reckless fiddling with the electoral system has raised widespread public concern about the integrity of Britain's electoral system."

"The electoral practices of the 18th and early 19th centuries, such as intimidation and fraud, risk becoming the hallmark of the 21st.

"Conservatives will be leading a cross-party campaign in both houses of parliament to challenge Labour's plans to hold the forthcoming regional assembly referendums by a compulsory system of all-postal ballots.

"We will also resist plans to use such ballots in any euro referendum or across all local elections.

"The Labour government has a clear agenda to throw away the ballot box and force all-postal voting on the British public irrespective of their wishes. Conservatives will protect people's right to vote in person and in secret."