Must admit i found it a non event. I did my RT practical in the UK having done my PPL in the states so i thought i might struggle but it was fine, i just read through the PPL coms book and had a look at CAP 413 and that was that. Certainly wouldn't be paying extra.
If i recall you get time to prepare with the RT exam route before you have to do it. If you have already done navs in UK prior to sitting it must be a doddle.
Best of luck.