Gaddafi loyalists join West in battle to push Islamic State from Libya

They are motivated partly by a desire to prevent Libya becoming another branch of Isil's caliphate - and partly by the knowledge that whoever retakes Sirte from Isil is assured prestige in the new political line-up.

“The stakes are very high, and for Libya, it may be the mother of all battles,” said Guma el-Gamaty, a Libyan politician involved in setting up the new government.

On Friday, the government said it was setting up a new national command centre to supervise the operation, as forces from different Libyan armed factions began encircling Sirte from a distance.

To the west, battle-hardened militia men from the port of Misrata - who honed their skills during a Stalingrad against Gaddafi's forces in 2011 - are gathering at Abugrein, a windswept desert crossroads.

Meanwhile, to the east of Sirte, around the drab oil town of Ajdabiya, troops are massing under General Khalifa Haftar. A Gaddafi-era maverick, he defected to the USA in the 1980s and then returned to join the rebels in 2011.

The fact that the Hefter and Misrata camps both fought to topple Gaddafi  in 2011 does not make them natural allies.

Ever since, they have been key players in the power struggle that has torn Libya apart, the Misratans seeing Heftar as another dictator-in-waiting, Haftar accusing the Misratans of being in hock with militant Islamists.

While neither description is wholly accurate, skirmishing between the two groups directly contributed to the power vacuum that allowed Isil a foothold in Libya last year.

Invited into Sirte by embittered ex-Gaddafi loyalists, they have now turned it into a "Mosul-on-Sea", terrifying its residents with a regime of beheadings, crucifixions and floggings.

Elsewhere in the anti-Isil coalition are even more unlikely partners. In southern Libya last month, a feared commander who fought on Gaddafi's side during the revolution threw his lot in with Heftar's anti-Isil camp.

General Ali Kanna, one of many Tuareg fighters recruited by Gaddafi for their desert combat capabilities, fled to neighbouring Niger with other loyalists after Tripoli's fall in August 2011.

Now he seeking to "wipe the slate clean" by joining the fight against Isil, according to Mattia Toaldo, a Libya expert with the European Council on Foreign Relations. 

"Some of the ex-Gaddafi era people are hoping that they can redeem themselves by joining the fight," he told The Sunday Telegraph.

Redemption, though, may come at a very high price. Sirte is now believed to be home to up to 6,000 Isil gunmen, led by senior commanders from Iraq and Syria, who are digging in for what may be a very bloody fight.

Last Thursday, Isil fighters launched a combined gun and suicide bomb attack on a checkpoint at Abugrein, killing two policemen and forcing Misratan commanders to flood the area with back-up forces.

Roads into the Sirte have been sown with landmines and roadside bombs. On the outskirts of town, fighters are building gigantic sand barriers. As well as suicide bombers, the group is also feared to be planning to use local residents as human shields.

Any invasion force can expect at the very least a re-run of the vicious urban fighting in Sirte last summer, when Isil pushed out militias from neighbouring Misrata through a combination of solid battlecraft and sheer fanaticism.

As one Misratan fighter told the Sunday Telegraph earlier this year: “Fighting Gaddafi’s people during the war was hard enough, but these Isil people are even fiercer. We have never seen anything like it.”

In its favour, the anti-Isis coalition has both greater numbers and better equipment.

General Heftar has around 7,000 troops on his side, as well as an air force. He also has new armoured vehicles given to him by Egypt, where his fellow military strongman, President Abdel Fattah el-Sisi, sees him as a useful ally amid Libya's chaos.

It is understood to be Heftar’s camp that has brought General Kanna into the fold, as part of a strategy to pacify ex-Gaddafi elements. In a further reconciliation gesture, Gaddafi’s former widow, Safia Farkash, has also been allowed back from exile to return to her home town in eastern Libya.  

Another key role will be played by Western forces, who have pledged the new Libyan government whatever military help it needs to oust Isil.

Plans to send up to 1,000 British troops to Tripoli as part of a joint British-Italian training mission now appear to have been shelved, amid fears that it would make the new government seem like the puppet of an occupying force.

Instead, the Western presence is in discreet groups of special forces, whose main task is liaising with local militias, and building up an intelligence picture of Sirte to assist with air strikes.

Yet even with outside help, it remains to be seen whether the campaign will draw Libya's different factions back together or simply drive them further apart.

Already, there are fears that the different factions are competing rather than co-ordinating with each other, prompting a warning from the new government last week that an "absence of unified leadership" could lead to a "confrontation between those armed forces." It pleaded with all sides to submit to a new "joint leadership" under its command.

Libya's militias are laws unto themselves at the best of times, and in Misrata, there is growing unease that Col Heftar's forces may be planning to take not just Sirte but also the valuable oil fields to the city's east and south.

"People are worried that if the Sirte operation isn't handled correctly, then this could be the start of a full-scale civil war," warned Mr el-Gamaty.