Thanks Ken for giving me a date to work from, I see now you mention it that the cap of the younger man does say GPO and I feel silly for not realising it sooner myself! I will look into it further, but I have read about the records in the link you sent me and it appears to me that the records would have to be searched by name not number or have I missed something there? I will have to do some more digging to try to find a family with 2 lads of about the right age at least I can narrow it down a bit more now.
Thanks again
Lidgett.