There has not been a financially successful British civilian light aircraft since WW2
Depending on your defintions of "succesfull" and "light aircraft", the BN2 Islander scores not too bad.
France and latterly Eastern Europe knock spots off us
France has done even poorer, their only success the DR400.
As for the demise of UK aviation industry after WW2, that is much more due to giving in to Uncle Sam than to giving in to Europe. Things went wrong around 1960, when "Europe" was still nowhere. RAF had no single reason to buy C130's, for only one example, the UK industry had perfect alternatives available. All politics, really.