Warren, thanks for posting these. I cannot claim anything other than having supplied a kit of parts to Bryan Jones and then passing to you for painting and photography!
The three 50' LNWR arc roof carriages are recent (re)-introductions to the Gladiator range. They are the D268 Corridor Third, D138 Corridor First/Third Composite and the D377 Passenger Brake. They are ex-Northstar products designed by Adrian Rowland. I think there was a limited release of them by Adrian, and Geoff Stratford released the passenger brake, but not the other two.
They will now be joined by another, the D216 Centre Brake Composite, which is currently with Warren for painting.
In a gratuitous plug I will point out that all will be available at Telford!