It is not a big deal to have the 'trophy' Browning deactivated and correctly certificated. Hand guns such as the Webleys etc are illegal and so is the possession of the ammunition. Only Military and Police have authorised handguns in the UK.
I think some of us are aware of PTSS that can be suffered by ex servicemen who have served in combat.Not a good idea for this man to retain firearms especially as it was retained 'as a reminder of his 22 fallen comrades'.
May be the judge had that in mind when sentencing this man.
As an aside Clint Eastwood made a film recently called American Sniper. A true story about the longest one shot one kill to date.
When the main character retired from the military he helped rehabilitate ex servicemen who suffered combat stress. He would take them shooting to the ranges. Mistake. He was shot dead by one of the patients he was helping.
http://www.bbc.co.uk/news/world-us-canada-21313208