There are numerous civilian "dunkers" in UK. Aberdean - Yarmouth
Fleetwood etc. One I would recommend is @ Andark Diving Nr. Southampton Tel: 01489 581755 - Andy who owns the complex is also a rotary pilot and runs a retail outfit selling wet/dry suits etc.
The civvy "Spare Air" will cost a lot less, is the same size and give about 10 minutes breathing near the surface. Best buy direct from California USA