The invalid cars and original* Southend Pier train were actually built at AC's other factory, opened in 1941 on Taggs Island**, one of the islands between Hurst Park and Hampton. An interesting history, at various times owned by Surrey, Middlesex, and (Mr) Kent.
* oops - the trains built for Southend Pier by AC Cars in 1949 were its second fleet, not the first.
** oops - it was Platts Island, further upstream, that moved from Surrey to Mddx (Greater London) in 1970 (and was therefore the only part of the Esher UDC to become part of Greater London). Thames Ditton Island moved the other way.