I'm not sure how it works but I believe you'll need to have a PAL holder on the set as the custodian of the gun if it's not a legally de-activated version suitable for blanks only.
There's also safety issues because even a blank pushes out a lot of high pressure gases from the end of the barrel that at short range (within a couple of feet) can be of concern. Your actors would need to be aware of this and treat the gun with a suitable amount of respect and consideration.
You may also want to tell us what city you're in. I'd be surprised if a local Enfield owner would not jump at the chance to have THEIR gun in a movie.