If you are offering military items for delivery abroad, for most of them you MUST obtain an export licence from the Dept of Trade and Industry.  If you are caught without a licence the maximum penalty set is either an unlimited fine or 10yrs jail.

And people do get caught:  An Essex company was fined £10,000 on 23 March 2006 for exporting military-listed body armour to various Middle East countries without the correct export licences. 

Direct links from here are not allowed, but go to the DTI website (dti.gov.uk) and search for Export Control Organisation.  You can e-mail them (see the contact webpage) or phone their helpline on 020 7215 8070.  You can also do a websearch for the "UK Military List" - if your goods are on it, you need a licence.