The latest legislation is The Explosives Regulations 2014:
Authorisation to store explosives
7.—(1) Subject to paragraph (2), no person may store explosives unless that person holds a licence for their storage and complies with the conditions of that licence.
(2) Paragraph (1) does not apply to—
(a)the storage of one or more of the following—
(i)no more than 10 kilograms of shooters’ powder;
(ii)no more than 5 kilograms of—
(aa)shooters’ powder; or
(bb)any hazard type 3 or 4 explosive, or desensitised explosive, which is not a relevant explosive, or a combination of hazard type 3 or 4 explosives, or desensitised explosives, which are not relevant explosives; or
(cc)a combination of shooters’ powder and any hazard type 3 or 4 explosives, or desensitised explosives, which are not relevant explosives;
(iii)no more than 15 kilograms of percussion caps or small arms ammunition or a mixture of them;
http://www.legislation.gov.uk/uksi/2014 ... ion/7/made
My interpretation of the above is that you can hold 15kg (33 LBs) of assembled ammo and percussion caps in addition to your Black Powder licenced holding (Paragraph iii). Subject of course to your FAC ammo holding, The same applying to Nitro powder (shooters powder) in addition to your 10kg (22 LB) holding without requiring a licence.