The Foreign Affairs Select Committee concludes: “Through his decision-making in the National Security Council, former prime minister David Cameron was ultimately responsible for the failure to develop a coherent Libya strategy.”

The scathing verdict comes just one day after Mr Cameron’s sudden announcement that he will leave Westminster immediately, breaking an earlier pledge to stay on as a backbencher.

In the report, MPs say:

* They saw “no evidence that the UK Government carried out a proper analysis of the nature of the rebellion in Libya”.

* There was no “defined strategic objective” – which meant a limited intervention to protect civilians “drifted into a policy of regime change by military means”.

* There was no attempt to “pause military action” when Benghazi was secured and seek a deal to protect civilians and reform Libya, with the UK instead “focused exclusively on military intervention”.

* Mr Cameron should have used Tony Blair’s “contacts and influence” to try to secure Gaddafi’s exit and a “negotiated solution”.

* Many Libyans had taken part in the Iraq insurgency and fought with al-Qaeda in Afghanistan, which meant the rise of militant extremist groups “should not have been the preserve of hindsight”.

* There was “insufficient action” taken to secure weapons abandoned by the Gaddafi regime, which contributed to the turmoil and “increased terrorism” across the region.

* Mr Cameron should have been required to issue a formal “ministerial direction” to intervene, noting the Chief of the Defence Staff, Lord Richards, “dissociated himself from that decision” in evidence to the inquiry.

* France led the campaign, noting: “UK policy followed decision-taking in France”.

Just six months after sending in the RAF and the Navy, in alliance with France – after the regime threatened to attack the rebel-held city of Benghazi – a triumphant Mr Cameron was mobbed by cheering Libyans on a visit with French president Nicolas Sarkozy

The two leaders pledged support for the future, proclaiming: “Your friends in Britain and France will stand with you as you build your country and build your democracy for the future.”

But the promise proved empty as Libya collapsed into a power vacuum, allowing Isis to seize control of part of the country and people-smugglers to send migrants towards Europe in rickety boats.

Barack Obama has called Libya the worst mistake of his presidency, apparently criticising Mr Cameron personally for the UK’s role in allowing the country to become a “s*** show”.

Crispin Blunt, the Committee’s Conservative chairman, said: “The UK's actions in Libya were part of an ill-conceived intervention, the results of which are still playing out today. Other political options were available. Political engagement might have delivered civilian protection, regime change and reform at a lesser cost to the UK and Libya.”

The international community must now get behind the United Nations-backed Government of National Accord to prevent the country descending into all-out civil war, Mr Blunt added.

Foreign and Commonwealth Office spokesman said: “The decision to intervene was an international one, called for by the Arab League and authorised by the United Nations Security Council. Muammar Gaddafi was unpredictable, and he had the means and motivation to carry out his threats. His actions could not be ignored, and required decisive and collective international action. Throughout the campaign we stayed within the United Nations mandate to protect civilians. 

“After four decades of Gaddafi misrule, Libya undoubtedly faces huge challenges. The UK will continue to play a leading role within the international community to support the internationally recognised Libyan Government of National Accord. 

“We have allocated £10million this year to help the new Government to restore stability, rebuild the economy, defeat Daesh [Isis] and tackle the criminal gangs that threaten the security of Libyans and exploit illegal migrants. HMS Enterprise and HMS Diamond are both currently deployed to support the EU naval operation to tackle illegal migration, people smuggling and arms trafficking.”