The Great Britain Project was a series of operations conducted by the Wilmarth Foundation against the Cthulhu Cycle Deities which occurred as the culmination of events in Brian Lumley's 1974 novel The Burrowers Beneath.
In the 1960's, the Wilmarth Foundation, a secretive group of humans from across the globe who were aware of and dedicated to destroying the Cthulhu Cycle Deities, became aware of a major incursion by the subterranean Shudde M'ell and his kin. Responding only after several years' research into the strengths and vulnerabilities of these underground creatures, the Foundation eventually made its move, but not before recruiting occult authorities Titus Crow and Henri-Laurent de Marigny into their ranks.
Having discovered that most tactics employed against the Cthulhu Mythos deities would only work once as these creatures communicated telepathically, transmitting their experiences to each other on or during death, the Foundation coordinated the efforts of the Great Britain Project to coincide with the assaults of the American Project, a similar campaign designed to rid the American continents of the same threats.
The Wilmarth Foundation's strategy consisted mainly of sinking deep shafts into the ground baited with captured female Chthonians, then blasting any of that species which came to rescue their kin with high-powered jets of water; as water acts like a powerful acid upon Cthonic biology, this was thought to have been a perfect weapon to use once the ambushes were sprung.
Ultimately, the Great Britain Project was successful, cleansing the whole of the British Isles of the Cthonic menace, although it was not without setbacks, notably when Professor Wingate Peaslee attempted to destroy Cgfthgnm'o'th, a lesser minion of Cthulhu, with an explosive mining drill. While this did kill the beast, much of the Foundation's equipment and several of their personnel were lost in the carnage unleashed by the dying monstrosity. Also, at the height of the Project's success, the by-then fleeing Cthonians discovered that by pooling their mental resources, they could bypass the magical defences employed by Peaslee's men, and their psychic "invasions" resulted in several suicides and so-called accidents. However, this too was only a stalling tactic, and the Foundation overcame it through the profligate use of Star Stones, artefacts which were anathema to the Cthonics, and whose protections the subterranean creatures were unable to breach.