Most zones are very happy to let people cross. Stansted once had a dreadful reputation, and yet are now very happy to help unless traffic levels are obviously a burdon.
It is easier to list those who seem to find GA a problem.
Luton is now great, but around the time they dropped out of LARS, there were some definite political games being played and GA got a very poor deal for a few months.
Birmingham are pretty dreadful neither offering transits nor anything other than then occasional FIS.
I have always been pretty sure that RT plays a part in determining if a clearance is going to be offered - at least when traffic volumes are high. Your ATC licence is placed at risk by every plonker who screws up in your zone, and RT is an indicator of sorts when it comes to the pilot's familiarity with operating in and around controlled airspace. Stumbling over lines is perhaps less important than not reading back every single item of information given to you in a very slow John Major accent whilst getting basic items like QNH wrong
Charlie