John Redwood has said Theresa May and other ministers in the Government would be breaking the law if they paid the proposed 'Brexit bill'.
The bill has proven to be a major bone of contention in the ongoing withdrawal negotiations.
EU officials have said the UK will need to pay a bill of €100 billion (£90 billion) to settle its outstanding liabilities.
Redwood, a prominent Leave campaigner and the MP for Wokingham, said any such payment made or authorised by the Prime Minister would be a breach of the law, as it has no basis in the statute book.
He told Sam Delaney and Katie Perrior: "I don’t think she can do that. Ministers have no legal power to give money away to rich countries like that.
"Ministers have various powers but have to live under the law. They can only distribute money if there is a law permitting them.
"There is no law giving them the right to give money to the EU, other than the treaty that allows them to make regular contributions."