The British campaign to overthrow Muammar al-Gaddafi's regime had its public face - with aircraft dropping bombs, or Royal Navy ships appearing in Libyan waters, but it also had a secret aspect.

My investigations into that covert effort reveal a story of practically-minded people trying to get on with the job, while all the time facing political and legal constraints imposed from London.

In the end though, British special forces were deployed on the ground in order to help the UK's allies - the Libyan revolutionaries often called the National Transitional Council or NTC. Those with a knowledge of the programme insist "they did a tremendous job" and contributed to the final collapse of the Gaddafi regime.

The existence of E Squadron is well known within the special forces community but has not hitherto been discussed publicly. It was formed five years ago to work closely with the intelligence service MI6, and is mainly involved in missions where maximum discretion is required, say Whitehall insiders.