Had this one a long time but never shown it here, so here goes.
Repair Party Electricity, belonging to ? ? Borough Council, well that's what I think the last two letters stand for. The first two letters B.G will be the town maybe.
With to the rear M for messenger, before this it had a life as an F.A.P, with M to the rear again,messenger.
No date on the shell but the liner is an HELMETS Ltd 1937.