Boris Johnson in newspaper
Boris Johnson says he will withhold Britain's £39 billion Brexit divorce bill if the EU doesn't reopen negotiations to agree more favorable terms. His pledge has been met with both derision and enthusiasm on Twitter.

Johnson, the frontrunner in the race to take over from Theresa May as British Prime Minister, told the Sunday Times that if successful in his bid for the role, he would bin the Northern Irish backstop element of the current exit plan and refuse to pay the Brexit bill until "there's greater clarity on the way forward."

The backstop has been a key barrier in seeing the Brexit deal agreed by May's government and the EU passed by British MPs.

"In getting a good deal, money is a great solvent and a great lubricant," Johnson said, adding that he'd ensure Brexit was delivered by the current deadline of Halloween 2019.

Twitter users were not convinced by Johnson's hardline pledge, with many pointing out that the £39 billion has already been agreed with the EU for money owed, and not coughing up the cash would be a major stumbling block in any future trade negotiations.

Some though fully backed Boris on his stance, urging the UK not to pay up because "we don't owe a penny."

Meanwhile, one of Johnson's several rivals for the top political post says he would pledge "hundreds of millions" of pounds to provide alternative solutions to the Northern Irish border issue. UK Home Secretary Sajid Javid told Sky News that if he becomes PM he would propose the huge payments to resolve the backstop "because economically it's right and morally it's right."