Boris Johnson has acknowledged the possibility of sending a plane full of cash to Iran to settle a historic £400 million debt.

The outstanding payment Britain owes has been linked to the continued detention of Nazanin Zaghari-Ratcliffe and other UK-Iranian dual nationals held in the country.

The debt relates to a cancelled order for 1,500 Chieftain tanks dating back to the 1970s.

Johnson-Says--Worth-Considering--Sending-Cash-To-Settle--400

Appearing before the Commons Liaison Committee, Mr Johnson was pressed by former foreign secretary Jeremy Hunt as to whether there was any obstacle to the UK simply repaying the debt.

Mr Hunt asked whether, if international sanctions meant such a payment could not be made through a bank, there was any other way of settling the obligation.

“If you can’t use a bank to repay it for various reasons why can’t we do what President Obama did in January 2016 and fly of a crate of cash to Tehran and just repay that debt?” he asked.

Mr Johnson replied: “It is certainly worth considering. But as you know there are complexities attached.

“It is also important to recognise that there are other UK-Iranian dual nationals in addition to Nazanin who form part of the equation and we have to be very sensitive to their needs as well.”

Nazanin's husband Richard Ratcliffe recently ended his 21-day hunger strike to try and force the British government to bring Nazanin home.

Ham & High: Richard Ratcliffe outside the Foreign Office on hunger strikeRichard Ratcliffe outside the Foreign Office on hunger strike (Image: PA Wire/PA Images)

Boris Johnson's comments came amid growing calls for him to settle the debt as a way of ending the ordeal of Nazanin – who has been held since her arrest in 2016 on charges of plotting to overthrow the government – and the other detainees. She has always denied all charges against her.

Two other former foreign secretaries, Jack Straw and Malcolm Rifkind, have also called for the money to be repaid.

Following talks with officials in London, earlier this week Iran’s deputy foreign minister Ali Bagheri Kani was reported to have said the two sides had agreed on the amount owed but the UK had raised the issue of “limitations on banking interactions”.

The prime minister said the government was working “as hard as we can” to secure Nazanin's release.

“I have nothing but admiration for the way in which she has dealt with it. It has been unbearable to witness and I know how much she wants to come home and to see her family,” he said.