Joanne ^ Sorry if I am telling you stuff you already know, but I think it best to cover all the bases
The transfer to Spanish plates is possible. Use a good, recommended gestor to do it for you. Of course checking how much they are charging you of course over and above the Taxes and ITV/new certificate etc.
But please be very aware that if you do this, although you will have a legal car to drive in Spain if you are resident for more than 3 months in any year (the old rule used to be that you could have a foreign plated car here for 6 in 12, but there is the issue of residency of course which is only 3 months max stay as a tourist The car will be devalued in the sense that if you wanted to take it back to the UK permanantly you would have to reverse the whole process (costing money), and that very few people will buy a RHD ex English car here - even if it is on Spanish plates. Basically it devalues it big time! As we found out to our cost… (We lost 1,000’s on our Cherokee Jeep.)
Just saying that it is best to research all options and go from there.
Good luck in what you decide to do