To own an antique firearm needs no licence and no storage security

To shoot requires a section 1 certificate and a suitable gunsafe. There is a small technicality in that originals may be shot "for testing purposes" without a certificate but finding a venue which will allow is not so easy.

To possess Black Powder requires an Explosives Licence and a suitable powder storage box.

Would recommend against using BP substitutes in an original.

Would recommend appropriate examination of the gun prior to using to be sure it is sound and in proof.