On board the RAF's Sentinel R1 spy plane over Libya

The RAF is flying reconnaissance missions over Libya with its Sentinel R1 spy plane, a modified business jet which uses radar to create accurate real-time images of what is happening on the ground.

Opposition forces are still locked in battle with those loyal to Col Muammar Gaddafi.

But without troops on the ground, how is Nato able to choose its targets, and make sure United Nations resolution 1973 is kept? Intelligence-gathering is key here.

The sun is setting over the Mediterranean as the ground crew at RAF Akrotiri in Cyprus make the final checks on the plane.

They were scrambled here from 5 Squadron based at RAF Waddington when the Libya no-fly zone was put into place.

Their task: to ensure that one of the UK's only remaining types of spy plane - the Sentinel R1 - could be sent into action.

Bulking out its slim frame is its sophisticated radar equipment which can scan thousands of square kilometres in minutes.

The bulky portion underneath the airframe is known as the "canoe" for its shape.

The plane itself is an adapted executive jet, much beloved of pop stars and oligarchs - although few will have chosen the same austere grey colour-scheme as the RAF.

There are no marble bathrooms or walnut walls inside these jets.

In place of rows of comfortable seats, three desks and three chairs face the side of the aircraft.

There are banks of computers with screens, and a small table and chairs for four other passengers.

Heavy weaponry

At a final briefing, the air crew are talked through their mission.

They will be flying the skies over Libya, focusing on coastal areas and towns such as Brega and Sirte.

The Sentinel crew were scrambled to Cyprus from RAF Waddington when the Libya no-fly zone started

Their job is to gather information on the movements of pro-Gaddafi forces and any heavy weaponry, as well as to keep an eye on normal civilian movements and look for any changes.

Once they have built up a picture of what's happening on the ground, the intelligence is passed on to Nato commanders enforcing the no-fly zone.

"The operations very much rely on the intelligence picture, and the information we provide adds to that picture and allows the commanders to actively look at where we want to go next, and use our assets in the most appropriate manner," explains Wing Commander Anne-Marie Houghton, the officer commanding 'A' flight, 907 Expeditionary Air Wing, now based in Cyprus.

"The US has similar capabilities, but the Sentinel itself is unique to the United Kingdom."

As darkness falls, we take off from RAF Akrotiri, the crew slipping smoothly into a well-rehearsed rhythm, right down to the number of ready meals waiting to be heated up in the tiny galley area.

There is also tea and coffee for the crew on the long flight, expected to last over 11 hours in total.

The RAF aircrew on board have asked to be identified only by their first names, for reasons of operational security.

"It's a very good aeroplane to fly, with very good performance," says the captain, James.

"We have our own tactics and methods of dealing with any air defences, and the job of the pilots up front is to monitor any air threat, and we have procedures to make sure that doesn't happen."

He jokes that the crew would "love to have the gold taps and leather armchairs" that are standard fit on this jet in its more glamorous incarnations, "but we'll make do with what we've got."

After several hours, the lights of Benghazi are clearly visible below us, as the radar scans towns up and down the coast.

'Interpreting the picture'

In Nato, only the US and UK have the capability needed to do this job - and it doesn't come cheap.

Five Sentinel jets, their ASTOR [airborne stand-off radar] and a through-life support contract cost the UK taxpayer £1bn over 10 years.

There are still sensitivities about operational security, and we are told we can't show the live images of the ground below which are being relayed and analysed on the screens by the two on-board analysts.

However, from some seven miles up, the radar produces images of startling clarity for the analysts on board, who are able to pick out areas they have looked at before and compare data on movements or any changes.

That information can then be passed on for commanders to choose targets, or just as crucially, to use in deciding what not to target to avoid any civilian casualties.

The Sentinel R1 is due to be retired in 2015, eight years after coming into service

Flt Lt Jim, the mission commander, tells us that they are currently looking at movements on the ground to identify pro-Gaddafi forces in the east of the country.

"We are able to give real-time analysis, and for us it makes it all worthwhile to know that we are able to protect civilian lives on the ground."

Chris, another of the airborne mission commanders, says that the information they can provide is proving vital in this campaign.

"In order to enforce the no-fly zone, we absolutely must understand the environment we are operating in."

There is still a risk to the crews from Libyan missiles, and these missions can be gruelling.

But the analysts say it is worth it.

"For myself, I thoroughly enjoy it," says Andy.

"It's one of the jobs that there's not many of us are doing, and we get to see a lot more - and can be part of something that is quite special really."

On board, I find it slightly surreal to be able to see so much of what is happening on the ground without setting foot in Libya itself.

After 10 hours, my eyes are beginning to close as we set off back to Cyprus.

These planes are due to be retired early to save money - in 2015 - a mere eight years after they came into service.

Yet the Sentinels and their crews are operating night and day over Libya and Afghanistan, providing vital information that can save lives in the air and on the ground.

Many are hoping that these high-tech spy planes may be granted a reprieve.