Well, of those companies listed, Leyland, we all know about! Vauxhall's still going, but making tanks?
Beyer-Peacock shut in 1966
Metro-Cammel now part of Alstom, so still capable?
Broom & Wade - Now Compair, so heavy engineering its ballgame?
Newton Chambers only now remains as Ronseal, 'nuff said! There is (?) a Churchill on display outside their old factory in Sheffield. (Wiki entry says it's been moved)
Gloucester Waggon are now owned by Babcock, so I'd say they've the capabilities
Dennis - well, possibly?
Charles Roberts - now Prorail, so highly likely.