The National Archives  
Ruskin Avenue
Kew
Richmond
Surrey
TW9 4DU
020 8876 3444

National Army Museum
Royal Hospital Road
Chelsea
London
SW3 4HT
020 7730 0717

Commonwealth War Graves Commission 
2 Marlow Road
Maidenhead
Berkshire
SL6 7DX
01628 507 200

Army Personnel Centre,
MS Support Unit, P&D Branch
Historical Disclosures MP555
MP 555
Kentigern House
65 Brown Street
Glasgow
G2 8EX

Regimental Headquarters
Grenadier/Coldstream/Scots/Irish/Welsh Guards
Wellington Barracks
Birdcage Walk
London
SW1E 6HQ

Ministry of Defence Medal Office 
Imjin Barracks
Innsworth
Gloucester
GL3 1HW

Defence Business Services JCCC (Joint Casualty and Compassionate Centre)
Commemoration Team
Room G35
Innsworth House
Imjin Barracks
Innsworth
Gloucester
GL3 1HW

Other things to look for:

Download a copy of our guide to tracing your British Army ancestry