Thanks for the comments folks. In fact, I'm not too worried about getting the RT "wrong" -- too many pro pilots and ATCOs have reassured me that it doesn't really matter how you say it, as long as the meaning is clear. I think the worry is more that I'll miss some vital instruction or bit of info and end up on the receiving end of yet another US-style tirade.. have my licence whipped away.. or worst of all, cause disruption or even an accident.
But it's good to know I'm not the only one with apprehensions!