Many people with German names living in the UK chose to change them during and after WW2, for obvious reasons.
As a German national, he was interned twice as a non-refugee alien (Category A). Index cards for the internment tribunals (National Archives, HO 396) are on Ancestry and FindMyPast, and he has two cards.
My interpretation of these is that he was first interned on 5 October 1939 at Olympia (in West London), home address 97 Northfield Avenue, Ealing. Then sent to Canada, as many internees were, due to lack of space in England – sailed 21 June 1940 on SS ‘Duchess of York’. When he returned to England on SS ‘Andes’ he was refused release and was re-interned, in the Isle of Man, on 12 May 1942. But he was released on 1 June 1942 to serve for the allied forces in the Pioneer Corps (see here --
https://en.wikipedia.org/wiki/Royal_Pioneer_Corps#Recruitment)
This was presumably when he married.
He also has a personal file at the National Archives in HO 405 – see this link ...
http://discovery.nationalarchives.gov.uk/details/r/C11122902It’s closed to public access, but you can submit a request for it to be opened under the Freedom of Information Act (FOI). It is an easy (and free) process. The request may or may not be granted. Sometimes it is granted with parts of the file redacted. The last one I applied for took about 4 months, but that was during lockdown.