Story highlights Ivan Rogers is an experienced diplomat who was due to play a crucial role

News is "a body blow" to the government said former deputy PM Nick Clegg

(CNN) Ivan Rogers, Britain's ambassador to the European Union, has resigned just months before Brexit negotiations are due to begin.

Before he quit, Rogers was due to lead the UK's negotiations to leave the EU.

Prime Minister Theresa May has said she wants to trigger Article 50 by the end of March 2017, paving the way for the process to commence.

Rogers' resignation was described by former Deputy Prime Minister Nick Clegg as a "body blow" to the Conservative government's plans.

It comes weeks after the EU's chief Brexit negotiator, Michel Barnier, warned Britain that it may only have 18 months to strike an exit deal from the bloc.

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