Thanks again for all the suggestions and various pointers. I've now had a chance to look further into this based on the above suggestions and the salient facts (most likely to be true) are:
The person in question, known as James Devauden, was born on 27 September. This is given on the record of death in 1974, and the 1939 identity card database. There is conflicting information about the year of birth, apparently being either 1891 (death record) or 1889 (1911 census and 1939 ID)
I cannot find a record for James Devauden, or anything close, in 1901 or 1891, nor can I find a suitable birth record for Leamington/Warwick in either 1889 or 1891. The ones I've so far examined can be ruled out by, for example, their subsequent appearance in 1911 or other records.
In 1911 he was living in Hereford, 30 miles due north of Devauden in Monmouthshire, where the parish church is St James (this makes a Google search for "James Devauden" the person, quite difficult!).
No one else in the world appears to be called Devauden, so surely this is not his real name.
He was a devout catholic who probably trained for the priesthood, but it's not known where, or when.
In 1939 his occupation was given as Visiting Manual Instructor, Mar College, Mechanical Engineer. 'Mar' refers to the Marist College in Hull, a catholic boys school, now closed.
Soon after 1939 he moved to Ulverston to work for aircraft engine manufacturer Armstrong Siddeley. He lived in Ulverston until his death in 1974.
The suggestion that he was a homosexual is quite plausible. He had no known relationships, save for the apparently platonic relationship, as a lodger, with my great aunt, from WWII until her death. As pointed out, homosexuality might be a cause for name change.
He left a will, and I'll obtain a copy, though I'm not hopeful of anything significant on it. He left £1800 and I'm pretty certain it would have been left to the Catholic Church.
Charles/Carl Albrecht is interesting, and definitely worthy of further investigation. However, with the significant age difference between James and Carl, the possibility of a homosexual relationship is perhaps not high, but who knows.
Thank you again for the help and suggestions, and anything further would be gratefully received.
Chris.