OK, so here's an update, and a very good lesson learned here as well.
I ordered the part on 1st November, having trawled around on Google and E-bay for a while I chose a seller called uab-gtv-trading, apparently based in Lithuania. It had quite a long lead time (not surprisingly) and the cost was £62.38, which is quite enough thank you very much, but it's an original part and should be fine for the rest of the life of the car.
I received various e-mail updates, as you do, and the other day I got an e-bay e-mail saying that the part had been delivered. However, there's no sign of it and it clearly has NOT been delivered. Interestingly, I received this e-mail at 13.31 on 17th November, and the e-mail claimed that the part was delivered at 19.43 on 17th November - so magically they delivered it more than 3 hours in the future!!!
After a GREAT deal of faffing around I managed to contact the seller, who got back to me 2 days later to apologise, and to cut a long story short they've agreed to give me a full refund. I will check that this does in fact happen of course.
So, today I did what I should have done in the first place, and contacted FRF Swansea, who answered the phone immediately, said they could get the part in the post to me next working day, and the all-in price delivered is £48.38 - which is roughly £14 cheaper than the e-bay seller! I also know that it will be a proper Volvo part, and having used FRF before I also have confidence that it will actually arrive.
Lesson learned - try Volvo (ideally FRF) first, it may well be cheaper and more reliable. I know there will be plenty of folk on here who will say "told you so" and you're right - as I say, lesson learned!
Hopefully it'll arrive next week and I can finally get it changed.
Cheers!