There is no national source for Italian records, they are kept at the commune level and since he was born relatively recently, there is no chance that they're online anyway even if you knew where he was born.
You need to know where he was born exactly, then you can write to that town and ask for a copy of his birth record.
His naturalisation record would be one source. The best document would be the application (held in HO 405). Here is the entry in the database:
http://discovery.nationalarchives.gov.uk/details/r/C14133385You will need to ask for it to be opened. This may be made more complicated by the fact that even if he and his wife are deceased, details of their living children may be included.
Alternatively, you could get a copy of his certificate:
http://discovery.nationalarchives.gov.uk/details/r/C12368320This will have less information but be easier to acquire as this document is already open. You can go directly to Kew yourself and look at it there, get someone to do it for you, or ask them directly for a copy (they're not that cheap but shouldn't be too pricey as I don't think these particular records have more than one or two pages in).
