I have sorted it. Racetech Direct can source them for around £14 each. The current relays being offered by some suppliers are a lower rating than the original red Siemans ones, I think some may also be in yellow. That's perhaps why the one I have put in is struggling to cope with the two fans going through one relay, as is the set up on the pre-cat. I plan to separate them at a later date. However, I noticed that another 3 or 4 of the relays, which are original, are also this type. Anyway sorted.