U.K. tax on Private Pensions

You need to complete a Form Spain - Individual (was called the FD9) which is here 

http://www.hmrc.gov.uk/gds/paye/attachments/81015_spain_indiv.pdf
You will pay tax in both UK and Spain until it has been finalised but the UK HMRC should refund the taxes you paid in UK.Don't hold your breath, though. HMRC is very slow at the moment. I contacted them by phone and they said they would only accept forms by mail but I think working from home means they don't check the mail. They told me they would reply in 28 days but it took 10 months to even acknowledge my letter. Then another 6 months to come back to me with yet another form to fill in.Still waiting since I sent that off in January this year.Private pensions, which are not government/crown pensions are only taxable in Spain under the dual tax agreement. Same with the state pension.

You will also need a letter from the Spanish tax authorities stating you are a tax resident in Spain which must accompany that FD9. I got mine by signing up with a clave from the Spanish tax site which then send you a letter with a code to enter in their website and you can download the form from there.

Thank you Marcliff that was very helpful. I know that HMRC are not good now as I originally sent the first form a year ago and received the letter in March this year. 
do you have a link to the Spanish tax website please, I’m afraid I only have basic Spanish although trying hard to learn it 

Yes, it's on here.

https://sede.agenciatributaria.gob.es/Sede/en_gb/procedimientoini/G305.shtml

I registered and they sent me a letter by post with a long code. Then you go back to this site and enter the code and they send you a SMS message with another PIN number. You can then download the fiscal resident code.

Thank you very much for your assistance 

A couple of years ago when I applied for and received my rebate from HMRC they sent it to me in Spain as a cheque!!

It cost a lot of money to have the cheque processed at my bank and they asked me to prove where it had come from.......

As of now I still don't think they pay rebates by bank transfer.

Steve 

Crikey it does seem that while it’s cheaper to live over here every opportunity is taken to get a share of our pensions 

Got annual tax refund cheque from HMRC just last week, using the Lloyds app was able to scan it in and the money was in my account within 24 hours.

I'd be surprised if other UK banks didn't have similar in their apps so maybe not looking hard enough?

Alternatively send them to me and I'll scan them in and transfer the proceeds for a modest fee.

Just found that I can pay a cheque on my banking app too 

I don't think you can scan UK cheques, or any  cheques with my Sabadell app..

Steve