Theresa May was dealt a significant blow on Wednesday night when one of her top cabinet ministers resigned over the British Prime Minister's approach to Brexit.

Andrea Leadsom, the Leader of the House of Commons and a prominent Brexiteer, said she could no longer carry out her duties because she “fundamentally opposes” May's latest Brexit bill.

“It is with great regret and a heavy heart that I have decided to resign from the Government,” Leadsom said in a tweet accompanying her resignation letter.

Leadsom's resignation could trigger further defections from May's ailing government ahead of the Prime Minister's fourth attempt to get her beleaguered Brexit deal passed.

May is facing increased pressure to resign; if she does, Leadsom is expected to throw her hat into the ring to become the next Prime Minister.