London (CNN) 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.

"I stayed in Cabinet to shape and fight for Brexit. There have been some uncomfortable compromises along the way, but you have had my determined support and loyalty in your efforts to deliver Brexit as our shared goal," Leadsom said in her resignation letter to May, which she posted on Twitter.

But Leadsom said she couldn't see a way forward with the new Brexit deal May offered on Tuesday. "I no longer believe that our approach will deliver on the referendum result."

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.

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