Keir Starmer scrambled to save the special relationship last night after his public falling out with Donald Trump.
He spoke to the US President after enduring a week of insults following his refusal to let US planes take off from the UK to attack Iran.
They discussed military co-operation in the Middle East and the Prime Minister expressed his 'heartfelt condolences' during the 20-minute phone call for the deaths of six soldiers in the conflict - a total that increased to seven last night.
But Sir Keir now also faces a battle on the home front as the Middle East crisis threatens his drive to cut the cost of living. He admitted last night that households were worried about how it will affect energy bills.
In another dramatic day:
- Iran named Mojtaba Khamenei - son of assassinated Ali Khamenei - as its leader
- Israel warned it would hunt and kill whoever was in charge of the Islamic Republic
- Tehran's streets were left like 'rivers of fire' after its oil depots were bombarded
- Iran retaliated by firing missiles into Israel, Kuwait, Qatar, Saudi Arabia and Dubai
Fears are growing that Britain will be hit by the highest wholesale gas prices in Europe, while oil prices could breach $100 a barrel within days after Iran effectively blocked the crucial Strait of Hormuz to tankers.
Britain faces paying more for foreign gas because it has less stored than other European nations, with just 6,700GWh (gigawatt hours) in reserve - enough for just two days.
During a visit to a community centre in London today, Sir Keir is expected to say: 'I know that people are worried sick for friends and family as the conflict in the Middle East continues. That's why we're working round the clock to keep British citizens safe.
'But people are also rightly worrying what this means for life at home - their bills, their jobs, their communities.
'No matter the headwinds, supporting working people and their families with the cost of living is always top of my mind.'
Ministers are already understood to be considering intervening to protect families from soaring bills, similar to the freeze announced after Russia invaded Ukraine.
One of Labour's main manifesto pledges was to lower energy bills by £300 by 2030 - a failure to do so would further damage its plummeting support.
In a sign of concerns at the top of Government about the impact of the Iran war on prices, Energy Security Secretary Ed Miliband rang consumer champion Martin Lewis at the weekend.
The founder of the Money Saving Expert website posted on social media: 'Just got off the phone after Ed Miliband called to discuss in detail the problems people are facing with domestic energy bills and heating oil.' Mr Lewis said that although energy bills were protected from the spike in wholesale prices, there was a 'potential ticking cost time-bomb' at the end of the spring when the summer price cap is set.
He added: 'If rates haven't dropped back down by May, and it looks like it'll stay high so the October price cap will rise too, and no cheap fixes are available, then things get into real problem territory. The Government needs to be (and I suspect is starting to) planning now for that eventuality in case more hard-core intervention is needed.'
Last week, Qatar shut the world's biggest liquefied natural gas (LNG) plant after an Iranian drone attack, and Israel hit Tehran's oil facilities yesterday, shrouding the sky above the capital in thick black smoke.
The strike prompted Iran to warn it would retaliate against oil sites in neighbouring nations if the attacks continued. Ebrahim Zolfaghari, a spokesman for Iran's central military command, told state TV: 'If you can tolerate oil at more than $200 per barrel, continue this game.'
Natasha Fielding, gas price expert at the commodity consultancy Argus Media, said: 'The UK's limited gas storage makes it more exposed to global gas and LNG supply disruptions in winter than the rest of Europe.
'The UK cannot rely on its storage to meet demand if it gets cold, so it must be able to secure LNG cargoes ahead of other European countries, no matter the cost.'
The Government insisted that gas supplies were not under threat, however.
The Department for Energy Security and Net Zero said: 'It is categorically untrue that the UK only has access to two days of gas supply. We have a diverse energy mix and are confident in our security of supply.'
National Gas, which runs Britain's gas network, said: 'Britain's gas storage levels are broadly in line with what we would expect at this point in the year and are comparable to this time last year.
'Storage makes up only a small part of Britain's diverse gas supply mix. The majority of our gas comes from the UK Continental Shelf and Norway, complemented by LNG, interconnectors with continental Europe, and storage.'
Yesterday's phone call between Sir Keir and Mr Trump was the first since the previous Saturday, when the PM turned down the US President's first request for US planes to take off from RAF Fairford in Gloucestershire and Diego Garcia in the Chagos Islands.
Even though Sir Keir changed his stance a day later, his initial refusal provoked Mr Trump to berate him repeatedly.
He began by saying he was 'very disappointed' in Sir Keir, then said he had 'not been helpful' and that it was 'sad to see' the special relationship in peril. He branded the UK 'very, very unco-operative', adding: 'This is not Winston Churchill that we're dealing with.' Over the weekend four B-1 bombers landed at RAF Fairford; the UK is sending a Merlin helicopter to the Middle East; and is sending HMS Dragon to protect the Akrotiri base on Cyprus.
The Prime Minister has scrambled to save the special relationship last night after his public falling out with Donald Trump
UK forces also took down an attack drone fired towards Iraq, the Ministry of Defence revealed.
But after the MoD said preparations to deploy the aircraft carrier HMS Prince of Wales were being stepped up, Mr Trump posted: 'That's OK, Prime Minister Starmer, we don't need them any longer - But we will remember.'
'We don't need people that join Wars after we've already won!'
Lord Dannatt, former head of the Army, said: 'It is so frustrating because America is an important ally of ours. They need us. We need them. And Keir Starmer standing on a narrow legal point has ruined that relationship.'
But Foreign Secretary Yvette Cooper said last night: 'The thing I've learnt doing this job is that you have to focus on substance and not on social media posts.'
Sir Keir is still coming under pressure to cancel the King's state visit to America next month over the President's behaviour.
Lib Dem leader Sir Ed Davey said: 'A state visit from our King would be seen as yet another huge diplomatic coup for President Trump. It should not be given to someone who repeatedly insults and damages our country.'