Best Car options moving to Spain

You cannot complete Spanish registration procedures for a car in UK any more than you could register a car in Spain with DVLA! 

"I know if we have a British registered car our British insurance will cover for 3 months" 

Not true, or at least not unless you tell your insurer exactly what you plan and they they specifically agree to cover you, but don't be surprised if they say no. 

If you leave UK come with the intention of becoming resident in Spain then an insurer can class you as no longer UK resident from the day you depart which would then immediately disqualify you from holding UK insurance.

If you buy a LHD car in UK then to drive it anywhere you will have to UK register and insure it then reregister it in Spain, you will also have to pay import tax based on it's value in Spanish terms, not UK or what you actually paid for it. 

If you want the simplest option then my advice is to fly to Spain and buy a Spanish car when you get here. 

Changing ownership of a Spanish registered car is nowhere near as straightforward as sending a slip off to DVLA and debts stay with the car so you risk becoming liable for any unpaid finance, fines and arrears of tax, and, as previously mentioned, you cannot drive it in the UK.
Some members have arranged a sale of their UK car with a UK garage, driven down and had the car transported back to the UK at a cost of €5-600. 
We brought our UK car with us and re-registered it here, at a cost, but it is not often recommended due to the restrictions in vision and problems with being on the wrong side for car parks and toll booths.
The price of used cars is higher in Spain but once you have made your first purchase you are back on a level playing field.

Thanks for your reply ,it’s something I’ll need to think about 

Thank you that’s very helpful ,have you any details on how they got their car transported back to the UK as that sounds like a possible plan . 

Can I clarify some details with you please as it’s a lot to think about .

If we come in our car and get residence then we can’t drive our car anymore as it’s British ?

Once we get residence we would have to drive a Spanish car I assume with a Spanish licence ?
sorry if I sound a bit dim but such a lot to consider and I want to ensure we make the right decisions and obviously don’t want to end up out of pocket 

Appreciate you taking the time to reply 

Thank you for the info it’s certainly seems like a great plan I’ll see if it’s possible to sell my car with the same proviso 

Our situation was different as we were travelling by plane, so we sold our UK car to a local garage then couple of days later got taxi to the airport.

We purchased a car within days of arriving in Spain, all very straightforward.

Click on Jim's Guides which are in a tab at the top of the page then scroll down until you get to the sections on driving, licences, buying and selling etc. I'd have a read through of all his guides as most of them will be relevant to you.

Thanks I’ve looked at bits on Jims Guides so just need to study them in depth