According to recently declassified files from the National Archives, scientists at Porton Down had been looking into new non-lethal weapons for Northern Ireland since 1971.

And after Bloody Sunday in 1972, officials were even more interested in ways of subduing crowds without causing long term harm to individuals.

Then they were asked to accelerate their work for use in Londonderry.

The military wanted weapons that would "incapacitate" demonstrators, allowing them to be captured.

Porton Down came up with a number of options: a powerful, fast-setting glue, super-slippery road coverings known as 'instant banana peel' and powders which would rapidly stiffen clothes, making movement impossible.

The scientists also researched a drug which would safely knock someone out.

The scientists at Porton Down had considerable experience in this area - they had already invented CS and CR gas.

But they rejected the idea of a gas, since there was the possibility that anything that made people unconscious very quickly risked killing them too.

Instead, they worked on an "auto-inject dart" - to be fired from a gun - which contained either an emetic or an anaesthetic and which was based on the vet's tranquiliser dart.

One of their favoured drugs turned out to be too dangerous. Files show the medical staff advised there was "an unacceptably high risk of death" with the vomit-inducing apomorphine.

The scientists also came up with an "entangler grenade", another idea they took forward.

This would explode in the air into coils of wire, landing on and immobilising protestors. The wire would be covered in fast-setting super adhesive. One idea was to add burrs which would also help trap people.

Royal Ordnance was asked to make up 1,000 of the grenades for testing but there the file ends - there is no indication of whether further tests were carried out.

A third idea was a "missile" which could take the place of the rubber bullet.

Scientists were very taken with the idea of modifying model aircraft so they could fly into a crowd at speed and knock down individuals. The cheapness of the idea was part of its appeal.

Despite some interest from military officials, there is no evidence that this idea was developed any further.

Despite little media attention, research in non-lethal weapons has increased sharply in recent years.

The Moscow Theatre siege in 2002 proved that the Russians had continued to work on anaesthetizing gas. At the same time, the tragic loss of life showed that they had hardly overcome the problems identified by Porton Down scientists.