The message was from Ebay.com (not ebay.co.uk), If you put "military policy" into ebay "help" it will bring it up.
It is here that its states :
"Prohibited Military Items in terms of this policy are articles or services specifically designed, developed, configured, adapted or modified for a military application"


Here is a cut and paste of their message to me :

We would like to inform you we have changed our policy for military items. You may be affected by this since you recently listed in a military item related category.

Due to the change, the sale of items regulated by the US International Trade in Arms Regulations is now prohibited.

Please read our military items policy before you list such an item again.

You can also find more information on which items fall under the US International Trade in Arms in the US Munitions List.

Please ensure your listings for military items follow these guidelines. If they don't, they will be removed. You may then be subject to other actions, such as a limitation on your buying and selling privileges, suspension of your account, and/or referral of the matter to the police.

Thank you for your attention to this issue.

Yours sincerely,

eBay