Steve - for public hangings, get in touch with your local Sealed Knotters. They have all the equipment and accreditations.
Try contacting some of the napoleonic/regency re-enactors who abound, through English Heritage - they are more than happy to offer advice, in my experience. Golly, my house was buit in 1780, you can borrow that if you like (even though it's 80 miles away)