Here in South Florida in the Sub-Tropics we have very intense sun. The most popular product used by RIB owners, Yacht Captains with RIBS and commercial yards is a product know as 303 protectant. It was developed by NASA, and as hard as it is to believe, it will stop 100% of UV fading if used on a regular basis. I use it every two months, just wipes on with no effort at all. Here is a US link to information on 303. It is available in the UK.
303® Aerospace Protectant 1 Gallon
Of course the optimal way to protect you RIB is to keep it covered at all times when it is not being used. I also always immediately do a wash down on the boat and a good dry. Nothing is ruin a boat faster that salt water left on the boat.