BFTA FT piston class is unique, in that Whiscombes and TX SR's etc are included along with any other springer/gasram.
So really it's a NON pcp class.
Not aware of any other comparable class in the UK.
In UKAHFT the above guns compete with PCP's.
In UK springer comps, they would have their own class, in enough turned up.
In terms of UK springer and UKAHFT, which i shoot, the tuning of guns varies a lot, here's a few examples.
Out of the box as manufactured.
Home tuned, with kits by Bonnie&Clyde/V-Mach/Maccari.
Home engineered internals by people with access to lathes/mills.
Guns rebuilt by, Bonnie&Clyde/V-Mach/Venom and others.
Guns built by keen shooters for themselves and friends who tinker as a hobby.
Basically all this tuning is really blueprinting the gun, and invoves minimising the tolerances and using quality lubrication.
For instance, your Prosport.
The delrin circlips, most would have them hand machined to ensure a perfect fit of THAT guns piston and comp tube, the piston seal would be sized so that the piston would fall down the comp tube when you took your finger off the port, all trigger sears would be polished, good quality lubes would be used sparingly, and a spring that had polished square ends with maybe thrust washers, and delrin guides.
Some may even have Ally pistons made, so that you can run a weeker spring to reduce the recoil.
Average Spring Gun Shooter