blue pigeon n.[late 18C–late 19C] (UK Und.)
1. a thief who specializes in stealing the lead from roofs [like an avian pigeon, the thief ‘perches’ on a church roof].
2. (also blue, pigeon) small off-cuts of lead or similar materials, taken from the job in hand and sold off as perks by plumbers.
3. (also bit of blue) a lead bullet.
[mid-19C] a stealer of lead from the roofs of buildings; such a thief poses as a journeyman glazier, plumber or other workman who gets to the roof, strips off the lead and hides it (often by wrapping it round the body) before leaving the house.
[late 18C–1900s] to steal the lead from a church roof; thus (blue) pigeon-flying, conducting such thefts.