The Tippmann E-grip is NOT legal in UK as far as i'm aware because it is pre-programmed with several different firing modes.
As well as standard semi auto, the E-grip can fire the Tippman in 3 shot burst (for each trigger pull)
Auto Response (one shot per pull AND one shot per release of the trigger)
Turbo (adding an extra shot per pull when you fire at a rate in excess of 4 bps)
And dear old Full Auto....
and i think there's another mode but my old brain fails me...
Also, i doubt that you'd get it in through customs and maybe land yourself in a heap of trouble doing so, especially as the Tippmann is a 'replica' style of marker, based on a H & K machine gun!
Just get yourself a nice semi-auto pink Evo Cocker instead
RE THE RESPONSE TRIGGER:
Depending on where you play and how fussy/informed/ thorough the marshals are at checking for trigger bounce you may or may not be able to use a RT trigger. RT triggers can be set so 'responsive' that the ram (behind the trigger) returns the trigger with more force than is needed to pull the trigger, so that holding your finger in a certain position causes the trigger to bounce.
This isn't 'full auto' as the trigger still has to complete a full cycle for each ball fired but there is technically no trigger 'pull' involved which is where the problem lies. The answer is to set the trigger to a moderate responsiveness where the trigger won't bounce, then lock it off with a spanner by tightening the nut on the RT valve.
Obviously be a responsible 'baller and DON'T take the spanner out onto the field so you can unlock the nut... if your Tippmann can't shoot fast enough in semi, then look for marker that can rather than 'bending' the rules and, quite likely, pi55ing people off!