The teddy bears, each about 412in high, were given to the twins in lieu of pocket money by their grandmother, Rosabell Rawlins. Each Christmas they would find their stockings brimming with as many as 50 tiny teddies. The 398 bears the boys had amassed by the time Mrs Rawlins died in 1931 are expected to fetch between pounds 30,000 and pounds 50,000 when they are auctioned at Sotheby's on Tuesday.
The twins, both of whom were later awarded the Military Cross, relied heavily on each other's company from early childhood and created an imaginary world inhabited by the bears, all of which were given names.
David and Guy used the bears to re-enact famous battles - they were particularly fond of Roundheads and Cavaliers - as well as sporting events. Sometimes the bears were even dressed as gangsters. The suitcase in which the tiny army was kept was propped open "so the bears could breathe" and went with the twins whenever they travelled abroad.
During the Second World War, the bear "leaders", Grubby and Young, accompanied their masters into battle. David, of the Black Watch (Royal Highland Regiment), was awarded the MC for "remarkable initiative and courage". Guy, who commanded No 5 Patrol in the Blue Nile area, won his award for "outstanding dash and courage". The honours were shared with Grubby and Young, which wear military sashes.
David was briefly separated from Grubby when he was captured by Rommel's troops at Saint Valery, France. The German soldiers, amazed to discover the small bear on his person, openly mocked David until an officer intervened and returned Grubby to his owner. And from 1942 to 1945 master and bear were interned in a German prisoner-of-war camp at Laufen.
After the war, the bears were kept in a customised mahogany display cabinet, fitted with platforms in the Campbell colours of black and yellow. They remained in Guy's house, where David was a frequent visitor.
David Campbell died in 1991, aged 81, and his brother two years later.
"The bears," wrote Sir Guy, "were our one joy."
The Campbell Bears will be auctioned at 10am on Tuesday by Sotheby's, London W1 (0171 293 5000)Reuse content