US President Donald Trump on Tuesday criticised British Prime Minister Keir Starmer as "not very helpful" with his stance on the joint American and Israeli strikes on Iran and praised European neighbours like France and Germany for their response to the war.

In a phone interview from the White House with 'The Sun' newspaper in London, Trump said he is "very sad" to see that the so-called UK-US special relationship is "not what it was".

He had earlier accused Starmer of taking "far too long" to allow the use of British airbases by US forces to attack Iran.

"He (Starmer) has not been helpful. I never thought I'd see that. I never thought I'd see that from the UK. We love the UK," said Trump.

"It's a different world, actually. It's just a much different kind of relationship that we've had with your country before. It's very sad to see that the relationship is obviously not what it was.

"This was the most solid relationship of all. And now we have very strong relationships with other countries in Europe," he said.

It came a day after Starmer was unequivocal in his stance against the UK joining the strikes on Iran, saying his Labour government did not believe in "regime change from the skies".

"The lessons of history have taught us that when we make decisions such as this, it is important that we establish that there is a lawful basis for what the United Kingdom is doing - that is one of the lessons from Iraq... They are the principles that I applied to the decision not to get involved in the offensive strikes by the US and Israel," he told Parliament on Monday.

"They are the principles that I applied separately to the separate decision on a separate request from the US to be able to take defensive action to hit the launchers for the missiles that are currently going into allies' countries in the region and threatening our citizens and service personnel. I stand by both decisions," he said.

Meanwhile, UK Chancellor Rachel Reeves delivered her Spring Statement budget in the House of Commons on Tuesday against the backdrop of the conflict and insisted the Starmer-led government had the "right economic plan" in an "uncertain" world.

"We will secure our economy against shocks and protect families from the turbulence that we see beyond our borders," she said.

The Iran war is expected to have far-reaching impacts on the cost-of-living crisis in the UK as household bills are hit by global oil prices, which are set for a major spike.