Jim
Your County Police Force will issue your licence to acquire Black Powder.
You will need to get a secure wooden box to store your powder. There are plans available to build these, or they can be purchased pre-built. Firms like Henry Kranks stock them.
You will be subject to an inspection by your FLO, in very much the same manner as when your FAC is granted/renewed. But admittedly a lot more formal.
The licence to transport Black Powder, is issued by the Health & Safety Executive. This is usually a formality after your licence to acquire has been granted.
I had to get a longer cabinet to house my 1878 Vetterli. I was lucky, I found a rusty s/h one. Cleaned it up, and bolted it to the wall alongside my existing, and put a couple of bolts between the two.
One satisfied FLO, and one happy Powder Hound.