Keir Starmer’s national security adviser is to travel to Washington as the UK government tries to persuade Donald Trump not to rip up the Chagos Islands agreement, the Guardian has learned.

Jonathan Powell, who negotiated the Chagos deal earlier this autumn, is drawing up plans to visit the US capital in the coming days, four government sources said.

Powell, who worked for a decade as Downing Street chief of staff for the then prime minister, Tony Blair, is seeking early meetings with Trump’s team ahead of the president-elect’s inauguration on 20 January.

One senior source said the trip, which may involve other government figures, would not be narrowly focused on the Chagos Islands but serve as an opportunity to introduce Starmer’s government to the incoming Trump administration.

UK ministers are concerned that Trump will block the deal to cede control of the Chagos Islands, where the US and UK have a joint military base, to Mauritius. Diego Garcia, the island where the base is located, will remain under UK control for at least the next 99 years.

The agreement was struck by Powell last month after two years of negotiations, which had been initiated by Rishi Sunak’s government.

The US election result has thrown the handover into question, however. Trump’s pick for secretary of state, Marco Rubio, warned in October that the agreement posed “a serious threat” to US national security by ceding the islands to a country allied with China.

Nigel Farage, the Reform UK leader, said this month that Trump’s team viewed the deal with “outright hostility” and would try to challenge it. “Diego Garcia was described to me by a senior Trump adviser as the most important island on the planet as far as America was concerned,” Farage told the Commons.

Powell, who is about to take up the national security adviser role, has been in Mauritius this week where the government he negotiated with has suffered a landslide defeat amid a wiretapping scandal.

In Washington, he will seek to persuade Trump’s advisers that the planned handover secures the future of the Diego Garcia base.

UK ministers have insisted that uncertainty over the islands’ legal status threatened the base’s operation and that the deal had support from across the US security system. Joe Biden’s administration has offered its public backing to it.

Stephen Doughty, the minister for North America, said this month that Trump’s administration would be briefed on the full details of the deal to “allay any concerns”.

Although 11 rounds of negotiations for it were held under the previous government, several leading Conservatives have been critical of the agreement.

Priti Patel, the shadow foreign secretary, has said it would “give away a key strategic asset” in the Indian Ocean. Tom Tugendhat, the shadow security minister, has claimed it could lead to China establishing its own military base in the Chagos Islands.

Mauritius has long argued it was forced to give the Chagos Islands away in return for independence from Britain in 1968. About 2,000 people were forcibly displaced from their homes in the 1960s and 1970s in what has been described as a crime against humanity and one of the most shameful episodes of postwar colonialism.

Five years ago the international court of justice issued an advisory opinion condemning the UK’s continued control over the Chagos Islands. David Lammy, the foreign secretary, has argued that without a deal a binding judgment against the UK seemed inevitable, jeopardising the future of the base.