Beclawat was the trade name for items supplied by Beckett, Laycock & Watkinson Limited.
The supplied the alloy window frames for many units, droplights for doors, and the sliding door mechanisms for interior doors.
For a company history see Grace's Guide.
The first illustration shows a Derby Lightweight unit for the West Riding.
Each of these series of illustrations show the parts that were suppled for the vehicles.
The next illustation shows a Swindon Works built 79xxx series Inter-City DMBS.
More Beclawat adverts can be found on the Railway Adverts website.