to get a service record of a british officer/enlisted man you need to get prove to the ministry of defence
(MOD)hes been dead for more then 25 years, this is done by getting his death cert,you then have to fill out an application form and send a cheque for £30 made payable to the MOD ,its a pain to be honest but can yield great results! heres the form you need to fill out for the MOD
https://www.gov.uk/requests-for-personal-data-and-service-records
i dont have the link for where you can get the death cert(thought i had it!) but i do know it costs about £9 to get it!
hope it helps a bit!