Sir Keir Starmer has appointed Jonathan Powell, a former chief of staff to Sir Tony Blair and background architect of the Good Friday Agreement, as National Security Adviser.

The veteran diplomat recently played a major role in talks over the Chagos Islands sovereignty dispute, which earlier this year saw Britain hand the territory over to Mauritius.

He will take over from Sir Tim Barrow in the position based in Number 10 after serving for 17 years in the Foreign Office and a decade in Downing Street.

The Prime Minister said Mr Powell’s experience in helping to broker a peace deal in Northern Ireland and working on “some of the world’s most complex conflicts” meant he was “uniquely qualified” to advise the Government on global challenges.

He will be expected to play a key role in forging links with Donald Trump’s new US administration, as well as helping to shape the UK’s response to conflicts in Ukraine and the Middle East.

The PA news agency understands Mr Powell has been appointed as a special adviser in a political capacity – a break from the norm that saw previous post-holders taken on as civil servants.

He is chief executive of Inter Mediate, a UK-based charity working on resolving international conflicts.

Mr Powell’s tenure as one of Sir Tony’s closest confidantes, between 1997 to 2007, came under intense scrutiny during the Hutton Inquiry into the death of scientist David Kelly.

He found himself in the media spotlight after the revelation that he had asked a security chief to change parts of the famous Iraq weapons dossier because some of the language posed “a bit of a problem” for Downing Street.

He is uniquely qualified to advise the Government on tackling the challenges ahead and engage with counterparts across the globe to protect and advance UK interests

His return to Number 10 is part of a wider shake-up under the new Labour administration that has seen former Blair-era figures brought back into the heart of government.

Last month Claire Reynolds, a former aide to Sir Tony and Gordon Brown, was appointed Sir Keir’s political director, and several senior ministers also served key roles during both the New Labour premierships.

“Jonathan has devoted his career to protecting the interests of the country,” the Prime Minister said after the appointment.

“Together with his experience helping to negotiate the Belfast (Good Friday) Agreement and work on some of the world’s most complex conflicts, he is uniquely qualified to advise the Government on tackling the challenges ahead and engage with counterparts across the globe to protect and advance UK interests.”

Thanking Sir Tim for his service during “some of the most challenging times in recent history”, the Prime Minister added: “I’ve no doubt he will continue to play a positive role on these issues in the future.”

There had been speculation under the previous Tory government that Sir Tim would move on to replace Dame Karen Pierce as Britain’s ambassador to the US, but she is expected to remain in post.

National security is at the heart of this country’s response to the many challenges we face and having an integrated response will be crucial to our success

Mr Powell said: “I am honoured to have been appointed as the National Security Adviser (NSA) to the Prime Minister. This is a hugely important role at a time where national security, international relations and domestic policies are so interconnected.

“As the Prime Minister has set out, national security is at the heart of this country’s response to the many challenges we face and having an integrated response will be crucial to our success. I look forward to advising the Prime Minister and working closely with ministers and officials in this new role.”

Despite Mr Powell’s experience, the decision to make a political appointment to the position of NSA is unusual and has already come under fire from opposition critics.

Paymaster general Nick Thomas-Symonds questioned Boris Johnson’s nomination of his ally Lord Frost for the role in 2020, on the grounds that the post-holder should be “independent, impartial (and) specialist”.

“That is why making a political appointment takes this Government into such dangerous territory,” Mr Thomas-Symonds, then-shadow home secretary, said at the time.

The Tories criticised the drafting in of “another Labour apparatchik” and highlighted past remarks made by Mr Powell relating to the Chagos Islands.

A Conservative Party spokesman said: “It’s disappointing the Government have appointed another Labour apparatchik to a senior role, sidelining an experienced general.

“Mr Powell’s previous comments about the unimportance of British overseas territories are extremely concerning and many will be worried that there is more to come.”

After the announcement of the British-Mauritian deal, under which the UK will retain jurisdiction of a strategically important air base on the island of Diego Garcia, Mr Powell dismissed concerns about relinquishing control of the archipelago.

He told Times Radio: “I don’t think we should be too worried about losing that bit of territory. We’re probably losing more to tidal erosion in the East Coast (of England) than that.”

He also highlighted that negotiations over the territory had started under the Conservatives, including James Cleverly who he said had “enthusiastically” engaged with the process as foreign secretary despite criticising the deal last month.