Hi Guys,
Thanks for the responses.
Ainslie; I know his full name is deffinitly Charles Frank Potter, so I don't think the lincolnshire guy with the extra 'C' is my g/grandad. It isn't the most unusual name which is why I find it a bit frustrating as to where to start - as you say he may not have even listed his middle name!
Nanny Jan; I'm afraid I haven't got a clue - I got the marraige certificate quite a while back and just looking through it tonight I clocked the 'soldier' thing and became curious
Redroger; They got married on August 20th 1919 (when he was 21)- oh wow okay, I didn't realise any of that - At least I know I can look specifically under the Pension section on ancestry

Bilge; I'm afraid we don't have any of the medals
Again, thanks so far for your advice guys :-)
Rachael