MI5 papers: Undercover conflict

Mind wars: The wills of German spies were broken, without physical violence, at a centre where the "omniscience and omnipotence" of the British security service was displayed.

In the few cases where suspects held out, they were shown obituaries of executed prisoners. None the less, 14 spies were executed because of information they gave.

Feathered fiends: Nazi commanders hatched a plan to use pigeons to spearhead an invasion of Britain. Lofts in occupied Belgium and the Netherlands were identified as bases for the feathered squadrons before they were sent with agents heading to Britain. Security officers believed use of the birds, which would be sent back with messages, had the blessing of the SS head, Himmler, identified by MI5 as a "life-long pigeon-fancier". The Army trained peregrine falcons to intercept enemy birds, two of which became "prisoners of war".

Sign language:

A crackdown on the defacing of telegraph poles was ordered by security chiefs during the 1940 invasion scare, because it was feared the marks may have helped enemy paratroopers. The signs on the poles were in fact the result of a survey in the area by an American oil company.