Museums can hold historic weapons fully working with a special licence,
Its not so much the type of weapon its the calibre of it, on the governments home office site there is a monstrous list of calibres you can own fully working without a licence (as long as you do not have any serious criminal record, firearms related criminal record and are over 18), you can have 2 identical revolvers, same make, model and year, one in .38 S&W you cannot own without a very special licence (ie a historic weapon) unless its deactivated, the other thats in .320 you can own fully working without a licence as part of a collection or display.
Its not just flintlocks and stuff like that either, there is quite a few semi auto pistols you can own, I have just bought a Martini Henry rifle from the Zulu wars, which any of you law abiding citizens out there can own as part of a display or collection.
I am not interested in just weapons, its all aspects of WW2, WW1 and the Zulu wars, just weapons are the most iconic of items to do with wars in my collection, if any of you want to know more, say you would like to own something from history, either deactivated, or working just pm me and I can put you in the right direction.
Here's an example I just found of one for sale in the UK
Here's a gun you can own without a licence in the UK fully working, I reckon she is enjoying firing this too much.