Pension

You do only pay tax once if over the threshold (lower in Spain),  you need to choose which is best based on your circumstances, talk to a professional is the best bet. My state pension is due next year, Unless there is a reason not to I plan to have it paid into my Wise account in sterling and then transfer to my Spanish account when needed and/or at a good exchange rate.

we have always had our pensions paid into our spanish bank account. It is difficult to beat the rate the uk govt uses, and it clearly demonstrates that you have an income to the spanish taxman.

Also likely to save you on bank fees if paid to Spanish bank directly.

No bank fees with Wise yransfer , they send the euros from an EU iban. Last 5000€ had a Wise fee of 4€ and the best rate around and no charges here at Sabadell. By using Wise as a buffer I will be able to choose where and when to transfer rather than a fixed date every month. No ties back in blighty so no advantage for us in using an UK bank account. 

We have always had ours paid into Spanish bank...good rate and we pay no bank charges. Also helps with residency applications as regular income. Personal allowance is only around 5500/6500 so you may pay a small amount of tax to Spain but not taxed twice.

Just out of interest does anybody know what exchange rate the UK Department of Work & Pensions use ?

Is it published somewhere on a regular basis ?

they use the market rate on the day its transferred so changes slightly each month

I thought they used the mid market rate the same as most transfer companies, please correct me if I am wrong.