A British Navy warship could be sent into Libyan waters to stop Islamic State smuggling arms out of the chaotic country.

In a dramatic escalation in the UK's role in Libya, Number Ten said it would seek UN approval to deploy a Navy vessel to turn back boats carrying both migrants heading for the EU and arms.

Crucially, Libya has now made a request to Western powers to operate in its territory - with David Cameron last night volunteering for Britain to take the lead at a summit of world leaders.

The warship would join four Navy boats already in the region on a NATO mission operating outside of Libyan territory.

In a dramatic escalation in the UK's role in Libya, Number Ten said it would seek UN approval to deploy a Navy vessel to turn back boats carrying both migrants heading for the EU and arms

For the first time, Downing Street raised the alarming idea that IS fanatics are using the migrant route to get weapons out of Libya and into the Med, though they stressed they were not destined for the EU.

The intervention by the UK could take place within weeks, subject to approval by EU and the United Nations - with officials expecting no objections.

Military planners have been deployed to Rome and are currently looking at how the mission will work.

Two different options include sending training ships for the Libyan coastguard to help tackle people smugglers, and sending ships with armed Royal Marines onboard to intercept vessels packed with weapons.

A navy source said: 'If it is going to be in contested areas then we will need to think about who needs to be onboard.'

Raffaello Pantucci, counter-terrorism expert at the Royal United Services Institute, warned of the danger of sending British vessels close to the shores of the war-torn country.

He said: 'I think ultimately the ships will come up against small vessels, at worst manned by criminals or terrorists. It is possible you could see them in firefights.

'It makes sense these ship will be deployed.'

A Government spokesman said that, last night, the Prime Minister had told the G7 summit that the migrant challenge is 'a global challenge requiring a comprehensive solution,'.

He said the PM told world leaders that Britain was willing to take the lead to help the Libyan Government 'build the capacity of their coastguard to intercept boats off the Libyan coast - both those carrying migrants and those carrying arms.'

For the first time, Downing Street raised the alarming idea that IS fanatics are using the migrant route to get weapons out of Libya and into the Med

The Government official added: 'We will now take an active leadership role in that process.

'Four military planners have deployed to Rome this week to the HQ of operation Sofia, the naval mission in the med, where they will work with other eu colleagues to agree a plan going forward for the Libyan coast guard.

'Once that is established we will then send a training team to assist the Libyan authorities in improving their coastguard maritime operations.

'Then once the relevant UN security resolutions are in place, we intend to deploy a navy warship to the region to assist in the interception of arms and human smuggling.'

There are currently four Navy vessels operating outside Libyan waters, working to turn back migrant boats. The fifth boat - a warship - will be added, with the intention of operating inside Libyan waters.

This is considered crucial in spotting boats before they can leave the Libyan coast.

Officials said that the Libyan Government had made an informal request for help for the first time. A formal request is expected within days.

Speaking en route to the G7, Mr Cameron said of the battle against Islamic State: ' I think we are being very straight about this. We are saying this is going to take time and it is difficult.

'For the very reason that we are not putting in Western ground troops, we are working with the Iraqi security forces, we are working in Syria with moderate opposition, and Kurdish forces and the rest of it. And this takes time.