A referendum on a "mini-Parliament" for Yorkshire will be scrapped in September if the Government is facing an embarrassing defeat, the Conservatives have claimed.

Bernard Jenkin, the Tory local government spokesman, predicted Tony Blair would use an Electoral Commission report on abuse of all-postal ballots to squirm out of holding an autumn ballot.

But the Government insisted referendums for a directly-elected regional assembly, with up to 35 members and a £500 million budget, were on track.

The row, in a Conservative-led debate on regional government, came after Labour's pledge to ditch all-postal ballots if the Commission ruled against them in September.

Ministers said that would delay the referendums - raising the prospect they would not be held before a General Election, which could be held in May or June.

The Electoral Commission is expected to look closely at the postal system following allegations of vote-rigging and ballot theft in Bradford.

West Yorkshire Police have investigated several allegations, but no criminal proceedings have been brought. Inquiries into two allegations are ongoing.

Mr Jenkin told MPs: "It's all too clear that, if the Government looks likely to lose the referendums by the time the Commission is due to report in September, then they will cancel them."

Local government minister Nick Raynsford confirmed there would be no all-postal referendums if the Commission produced "convincing evidence" this would be unsafe.

Constitutional Affairs Minister and Shipley MP Chris Leslie said in that "unlikely event" the legislation would have to be started again from scratch to allow for a traditional ballot.

He said: "The plan always was to hold the referendum in the autumn and it still is."