LONDON (AP) — As Brexit enters its endgame, the big divide is not between the U.K. and the European Union, but between Britain's government and Parliament.

Since Britain struck a divorce deal with the EU late last year, the executive and legislature have been at war.

Prime Minister Theresa May is struggling to win backing for the agreement ahead of Parliament's vote next week while lawmakers try to grab control of the Brexit process.

The battle has destabilized a country without a formal written constitution and where democracy rests on centuries of law, precedent and convention.

London School of Economics Professor Iain Begg said Thursday that Britain is "getting very close" to a constitutional crisis.

He says "if Theresa May loses the vote next week, we don't actually know what happens next."