I read this novel in the early 1990's. I think it is written in first person diary form, and it's as much a satirical comment on urban life in Scotland as a science fiction story. The protagonist is an alien who has taken over the body of a Scottish trainee solicitor. The aim is to spy out Earth's defences, but the irony of him not being well placed to do that is commented on. I can't remember if he is in contact with any fellow alien spies or not. I think that very gradually the characters of the alien and the host body merge and in the end the alien ends up in a happy relationship with his girlfriend and has more or less become human and has abandoned his role as a spy.
Some random things I remember:
The host body's mother is not very bright and keeps making the same exclamations over and over again, much to the puzzlement of the alien.
This detail for some strange reason is the thing I remember best: in his work as a trainee solicitor the protagonist has dumped on him the legal job everyone in the practice hates most, that of untangling the immensely complicated ownership of the lease of a little shack used for meetings by (I think) the Kelvinside Old Comrades Association, a war veterans' group. He finally does it, a personal triumph, only to find out that the land had been bought at a handsome price for redevelopment so he needn't have bothered.