Dogged by party divisions, endless plotting and caught in the quagmire of Brexit, British Prime Minister Theresa May's political obituary has been written many times.

But the Conservative leader has proved a remarkable survivor.

She moved within months to start the Brexit process and sought to bolster her domestic political position with a snap election in June last year.

This spectacularly backfired and she lost her majority in the House of Commons, leaving her reliant on a Northern Irish party to govern.

Since then, her party's pro- and anti-Brexit factions have taken turns to flex their muscles, seeking to influence her strategy and bringing her government to the brink.

Each time they have proved unwilling to deal the fatal blow, but tensions are rising again as the Brexit negotiations reach their final stretch.