BEagle
I've just received a reply from the CAA - this confirms what you say except that I need to take a full JAA skills test rather than the rating renewal check.
Also they state
"As your email suggests, your RT licence is valid as long as you PPL(A) is valid and therefore there are no renewal requirements needed"
Which again contradicts guidance documents on their own website. So I shall keep on pursuing them until they can give me a satisfactory answer and identify which of their documents are correct and which are not. I will post the conclusions of my investigations on this forum when they are complete.