Boris Johnson, the leading candidate to succeed Theresa May as Britain’s next prime minister, said he would withhold a previously agreed 39 billion pound ($50 billion) Brexit payment until the European Union gives Britain better exit terms, Reuters reports.

“I always thought it was extraordinary that we should agree to write that entire cheque before having a final deal. In getting a good deal, money is a great solvent and a great lubricant,” Johnson told the Sunday Times.

The 39 billion pounds represents outstanding British liabilities to the EU, which would be paid over a number of years according to the withdrawal agreement negotiated by May.