I know of 2 pilots that have done this. 1 has since retired but had to stop as the CAA seem to make it more difficult as time goes on. The other is still around but has only done it a few times.
As well as the CAA rules you must be tested and approved by the BPA.
I have sat left seat in a long ranger watching 5 guys jump out at 5000 ft, mad!!!
Jarvy