Career diplomat Sir Tim Barrow is a "seasoned and tough negotiator" who will help the Government make a success of Brexit, No 10 has said.

Downing Street officially confirmed the former ambassador to Russia will replace Sir Ivan Rogers as the UK's top civil servant in Brussels from next week.

It follows the surprise resignation of the UK permanent representative just weeks before the expected start of Brexit withdrawal negotiations.

Sir Tim said: "I am honoured to be appointed as the UK's Permanent Representative to the EU at this crucial time. I look forward to joining the strong leadership team at the Department for Exiting the EU and working with them and the talented staff at UKRep to ensure we get the right outcome for the United Kingdom as we leave the EU."

Prime Minister Theresa May approved the appointment on the advice of Cabinet Secretary Sir Jeremy Heywood.

A Downing Street spokesman said: "We are delighted that Tim Barrow is taking up this role. A seasoned and tough negotiator, with extensive experience of securing UK objectives in Brussels, he will bring his trademark energy and creativity to this job - working alongside other senior officials and ministers to make a success of Brexit."

Foreign Secretary Boris Johnson said Sir Tim was "just the man" to secure the best deal for the UK.

He said: "Tim Barrow has been invaluable since I joined the Foreign Office in July and I want to personally thank him for his relentless energy, wise counsel and steadfast commitment.

"He is just the man to get the best deal for the UK and will lead UKRep with the same skill and leadership he has shown throughout his career. I wish him all the best."

Sir Tim was appointed political director general at the Foreign Office last March after leaving his role in Moscow.

He has had two previous stints working as part of the UK's Permanent Representation to the EU (UKRep).

Brexit Secretary David Davis said: "UKRep will have a crucial role to play in the negotiation over the UK's exit from the EU, and Sir Tim Barrow will add to the already extensive experience it brings.

"His knowledge of Brussels means he will be able to hit the ground running at a vital time, and steer UKRep throughout the negotiation period. I am confident that with his help, the UK will be able to forge a new relationship with the EU that works to the mutual benefit of both sides."

But Ukip said the role should have been given to a "committed Brexiteer".

Brexit spokesman Gerard Batten said: "This appointment is a disappointment because the last thing we need is another career diplomat wearing a Brussels jersey.

"The Foreign Office needs a complete and revolutionary shake-up for it must begin to reflect the stated desire of the British people to leave the EU.

"We need to remove career diplomats who have been so spectacularly unsuccessful in protecting British interests for the last 44 years.

"In their place, we need committed and sincere Brexiteers, people who actually want Britain to leave the EU and are prepared to make it happen. We also need more people like this in Government who will ensure the same."

Sir Ivan had hit out at the "ill-founded arguments and muddled thinking" of politicians in a fiery resignation letter.

Labour called for the Government to set out a clear timetable for the publication of its Brexit plans in the wake of the resignation.

The party's Brexit spokesman Sir Keir Starmer said Sir Ivan's resignation was likely to be a "significant loss" for Britain and raised "a number of serious questions" about the Government's preparations for the talks, which Prime Minister Theresa May has said she will trigger under Article 50 of the EU treaties before the end of March.

Sir Keir said: "I welcome the appointment of Sir Tim Barrow as the UK's new Permanent Representative to the EU. It is of course vital that there should be no vacuum in such an important role and that the new Permanent Representative should be someone with a strong and distinguished record of service as a diplomat.

"But a number of fundamental questions remain unanswered. In particular, Sir Ivan Rogers' confirmation that the Government lack a plan for Brexit and his statement that the UK does not have a proper and effective negotiating team in place."

Ukip former leader Nigel Farage said: "Good to see that the government have replaced a knighted career diplomat with ... a knighted career diplomat."