gonna sound stupid but howmuch fuel is in the car? i had this on my fiesta si and couldnt work out what was wrong with it! turns out i had a faulty fuel gauge (had not had the car long) so just above the rd was actually pretty much empty, the car would start and idle fine but miss under load or bliping the throttle, my guess would be some crap at the bottom of the tank was sticking to the filter on the pump, filled up with fuel no problems. may be worth a try just as if it doenst work its not like you wont end up using the fuel when its fixed.
oh and the RR centre youve taken it to sounds CRAP.