Nazi-trained homing pigeons were the target of British covert operations during WWII, it has emerged.

Scores of lofts of the message-carrying birds were pinpointed by MI5 agents in 1940 across Belgium, West Holland and the Balkans.

The airborne threat was believed to be the pet project of SS chief Heinrich Himmler - who was known by British intelligence as an avowed pigeon fancier.

Under interrogation, captured "German pigeon personnel" told how the birds were a vital component of Hitler's plans to invade Britain.

The MI5 report on the phenomenon, released with a batch of wartime secret service documents this week, said: "From these prisoners of war it was learnt that it was anticipated that the birds would be used to convey information obtained by short-term pre-invasion agents."

To counter the menace, MI5 tamed and trained its own crack force of peregrine falcons, with the aim of felling incoming pigeons.

According to documents now held at the Public Record Office in Kew, London, at least two of the captured pigeons became "prisoners of war".

Displaying humor in the midst of adversity, an intelligence officer marked in his report: "Both birds are now prisoners of war working hard at breeding English pigeons."

The new Army Pigeon Service Special Section birds of prey were used to set up an airborne net over the Scilly Isles early in 1942 following sightings of pigeons disappearing towards France.

The MI5 report notes Britain's new anti-pigeon force would patrol for two hours at a time over the islands off the Cornish coast.

It says: "This was a great success. The falcon flying high above the Scillies could watch not only a part of one island, but the whole group, and any pigeon flying over them would be attacked."

Agents had found that the Nazi party had taken control of all pigeon lofts in Germany after it assumed power, while Himmler had ordered the use of pigeons by his own Gestapo security police.

The British document notes: "It is said that Himmler, who has been a pigeon fancier and enthusiast all his life, is the head or president of the German National Pigeon Society.

"And he has brought his enthusiasm for pigeons into the Gestapo, who are said to use this form of communication both in Germany and in the occupied countries."

Intelligence officers also investigated ways in which pigeons were deposited in the UK. They believed some were carried in by individuals, and that some were dropped off in baskets by high-speed E-Boats and submarines.

Dropping pigeons by parachute was also identified as a possible method of their entering the country.

German Recon Pigeon

WWII security service operatives were also on the look-out for:

·        Suspicious marks on telegraph poles
At the height of fears of a German invasion, reports of markings on telegraph poles prompted a major investigation. MI5 eventually concluded, however, that the marks were the work of the Anglo-American Oil Company ... or boy scouts and girl guides.

·        Crop cutting
Farmers cutting crops out of season, or in unusual patterns came under suspicion of trying to convey messages to airborne craft, or of providing runways for the enemy.

·        Annotated maps
Marked maps, strange notes, or even hanging out white linen could have lead to investigation by MI5's operations section.