If you believe that ADSB is reliant only upon GPS with no ground infrastructure in the UK, then you should post your pilot licence back to the CAA immediately. (If you have one)
One could have written something informative in the same amount of time.
In any case, TCAS (of any sort) is well outside the scope of any PPL training syllabus.
ADS-B is reliant on GPS because it broadcasts a GPS-derived position.
But ADS-B is a long way away in Europe. I don't think Mode S can be avoided at all if one is flying IFR outside the UK, although I would not be suprised if they exempt IFR traffic OCAS (i.e. Class G) in the UK. In any event, nobody cares what you do in Class G - you can fly IFR non-radio so VFR v. IFR is largely in your head.