Remember you have to declare the sale and the gain to the UK tax authorities. You will be able to claim your CGT tax free allowance (X2 if the place is jointly owned) you be also be able to claim taper relief depending on how long you’ve owned the place. Then you will face UK tax on the gain at 10%, 22% or 40% depending on other taxable income and the gain made. You can, of course, deduct spanish tax paid from your eventual liability. This should still work out cheaper than the old spanish rate.
Be careful if you sell and do not declare to the UK taxman. If you bring the money into the country and deposit it building societies now routinely report any large interest payments to the revenue. These are matched with previous declarations and you will be asked to explain the difference.
Best to keep the dosh in Spain if you don’t want to report it in England.