LONDON (REUTERS) - Britain is to appoint career diplomat Tim Barrow to replace Ivan Rogers, its top envoy at the EU who quit this week with a blistering attack on the government's plans to leave the bloc, the Financial Times reported on Wednesday (Jan 4).

No official comment was immediately available.

Barrow, a former ambassador to Moscow, will play a key role in the Britain's Brexit negotiations.

He was Britain's ambassador to Moscow until 2015 and in March 2016 became political director at the Foreign Office. He has formerly acted as first secretary at UKRep, the effective British embassy in Brussels.

Barrow's appointment, if confirmed, will mark a swift transition after Rogers' high-profile resignation.

Rogers said in a letter to his staff that Prime Minister Theresa May's negotiating objectives were as yet unknown and told them: "I hope you will continue to challenge ill-founded arguments and muddled thinking."

May intends to launch the two-year process of negotiating to leave the bloc by the end of March, beginning what is expected to be some of the most complicated international talks Britain has engaged in since World War II.

She has so far said little publicly about Britain's negotiating position, arguing that to do so would weaken London's hand in talks.