The Foreign Office was facing embarrassment tonight as its first rescue flight for British nationals stranded in Libya was stuck on the tarmac at Gatwick with a mechanical fault.
With hundreds of Britons waiting to be flown out of Tripoli airport, the Boeing 757 had still not left after 5pm. It had been due to leave at 12.30pm.
The delay came after British nationals and shadow foreign secretary Douglas Alexander accused the Foreign Office of taking too long to respond to the chaos that has engulfed Libya.
Foreign Secretary William Hague promised to send as many rescue flights to Libya as were needed to evacuate Britons wanting to leave.
Two were due to leave today and a third - if necessary - early tomorrow morning.
At least 300 Britons are in and around the Libyan capital Tripoli, while up to 170 more - mainly oil workers - are in remote desert camps at risk of attack as violence continues.
Mr Hague said that, as well as laying charter planes, he was not ruling out the possibility of using military flights "without permission".
Royal Navy frigate HMS Cumberland is on its way to the Libyan coast to evacuate Britons around the Benghazi area.
But in a statement this afternoon, Mr Hague insisted: "We are taking every action to get the remaining British nationals in Libya out of harm's way."
The first of the Foreign Office flights - free for British nationals, unlike similar flights to and from Egypt recently - was hoped to return to the UK later today.
However, the 200-capacity Boeing 757 still was still at Gatwick at 5pm despite previously being billed to depart for Tripoli at 12.30pm.
Foreign Office minister Alistair Burt said the plane, which was meant to arrive by 9.30pm, was being fixed.
"Sometimes planes develop faults through nobody else's fault or error," he told the BBC.
"We will hopefully get those planes out as quickly as possible."
At Tripoli airport, British consular staff were issuing UK nationals with boarding cards, as well as crisps, bananas and water.
Hundreds of Britons have already left the country on commercial flights over past week or so, but many scheduled services have been cancelled in recent days.
"We will send as many planes as necessary to bring home British nationals," Mr Hague said in a statement.
He went on to indicate that military flights might yet be laid on.
"Our preference clearly is for people to leave on commercial flights as they have been doing, or on our specially-arranged charter flights as they will now be able to do, rather than to send in military flights without permission, which is obviously riskier for the safety of all those involved, although we don't by any means rule out doing that," he said.
The Foreign Secretary warned that oil workers living in desert camps were at particular risk and urged them and their employers to make contact with the Foreign Office if they had not already.
"These camps are remote and isolated, they are scattered over a large distance and are dependent for food and water on supplies from Libyan cities that have been severely disrupted by the violence and unrest," he said.
"Some we know have been subjected to attacks and looting. They are in a perilous and frightening situation.
"We are working intensively on a range of options to secure their safe passage from Libya, working with other countries whose nationals are in the same position."
Earlier today, one oil worker said he and his colleagues had been left by the British embassy without protection.
James Coyle, who is based between the capital Tripoli and second city Benghazi, said: "We are living a nightmare and we have asked the British Government and they have just totally ignored us.
"They don't reply to emails, they have cut off the phones to Tripoli. We told them the situation three days ago - they never even replied to us.
"We have been left without any protection whatsoever."
He added: "We are living every day in fear of our lives as the local people are armed with AK45s and AK47s."
A British woman who had had difficulty leaving Libya said she and a Portuguese friend were helped out of the country by Portuguese embassy staff yesterday.
"There was nothing at all happening with the British Embassy. We felt very isolated and very out there on our own," the unidentified woman told BBC Radio 4's The World At One.
"There were three people from the Portuguese embassy there, they had our names on a list and they got us on to a plane."
Hundreds of Libyans have been killed in violent clashes between anti-government protesters and forces loyal to dictator Colonel Muammar Gaddafi in recent days.
Colonel Gaddafi is refusing to relinquish power, vowing to fight to his "last drop of blood".
Mr Hague warned Libya that its leaders would be held to account for alleged human rights abuses.
He said: "We are greatly concerned about the loss of life in Libya and their government's failure to protect its own people - indeed, their behaviour of launching attacks on their own people.
Mr Hague added: "We believe those who commit or sanction crimes or human rights abuses in Libya should be held to account. That is our clear message and warning to them in the future.
"To those in Libya who may be guilty of such acts, Britain and our partners around the world will be doing everything to hold them to account in future."