Service Records
Tyres / Nacluv
If you are the NOK and can supply your relatives name, you will be able to obtain a copy of his service record from the RAF Disclosures Office at RAF Cranwell, Lincs. The bad news is they will charge a fee, last I heard about £30.
If you are not the NOK (or the individual is still alive) you will need the NOK / Serviceman's written authority to obtain a copy of the Service record.
Nacluv
The Air Historic Branch (RAF Northolt) will be able to give you further details on the mission in which your Uncle was lost.
TT