If I've got it right, and courtesy of Familysearch, Malcolm Leon Cowin's gt gt grandfather was married in Kent:
Matthew Cowin m. Francess Boorman 24 Nov 1810 New Romney. He was dead before the 1841 census so without proper genealogy it's not obvious where he came from. Can't find a likely baptism in Kent or elsewhere in England. Familysearch has a baptism in German, IOM in 1783 that would be suitably aged candidate. There is also a burial in German in 1789 but Lawson's burial index doesn't indicate that this was an infant, and it could possibly be the Matthew baptised (FS) German in 1758.

Anyway, nothing conclusive and I think I'll leave it there. Was fun looking!