London CNN  — 

A senior UK government minister has warned there is a “50-50” chance Brexit won’t happen, if Prime Minister Theresa May’s deal is voted down in Parliament next month.

International Trade Secretary Liam Fox, a prominent Brexit supporter, told the Sunday Times that the only way to be “100% certain” Britain will leave the European Union is if ministers back the deal.

The UK is scheduled to exit the bloc on March 29 next year. But the road to departure has been a bumpy one – with the latest hurdle May’s beleaguered withdrawal agreement, negotiated with the EU last month.

Liam Fox was a prominent supporter of Brexit in the runup to the 2016 referendum.

The deal needs the backing of UK ministers to go ahead, and a vote was due to be held earlier this month.

But just hours before the vote was to happen, May pulled the plug when it became clear she would lose “by a significant margin.”

The crucial vote is now planned for the third week of January. If it fails, Brexit will be thrown into serious doubt, said Fox.

“If we were not to vote for that, I’m not sure I would give it (Brexit) much more than 50-50,” said Fox.

He called on fellow Conservative Party members to back May’s deal, adding that failure to do so would be “incendiary.”

Juncker to UK: ‘Get your act together’

The biggest sticking point among ministers opposed to the deal is the Northern Irish backstop. The backstop is an arrangement designed to ensure there is no return to a “hard border” between Ireland – which will remain part of the EU after Brexit – and Northern Ireland, when the UK leaves the bloc.

After postponing the vote earlier this month, May made a dash to Europe to seek further reassurances from leaders over the backstop – and placate ministers back home.