In Biggles Nets a Fish, Colonel Barclay was a British Army officer who was responsible for the security of the Harwell atomic pile and other atomic research stations including that at Heatherstone Moor. When Major Booth brought in a micro-film of secret plans which must have been photographed by someone with access to the top secret work at Heatherstone Moor, Barclay and Major Charles approached Air Commodore Raymond to look at the air angle because the film had been dropped by an aircraft over Germany.
Barclay accompanied Biggles back to Heatherstone Moor and provided Biggles with all the background information about the facility, including details about its neighbour, a Czech named Felceman who owned the fishing rights on the stream which ran near to the research station. Later Barclay told Biggles that his scouts had detected that Felceman had been seen trying to fit a long range tank to a Gipsy Moth which he owned. Barclay also supplied Biggles with a photo of Felceman which helped Biggles recognise him as someone he had met and helped during the war.
Partly using the information supplied by Barclay, Biggles uncovered Felceman's role as the courier of the micro-films which were smuggled out of the research station by the spy through a capsule thrown into the stream. Felceman agreed to help Biggles trap the spy. When this was revealed as Doctor Mills, the deputy director of the research station, Barclay was on hand to take him into custody.