The VPN using a Raspberry Pi is a nice idea and should work fine for you for BBC iPlayer etc. These services get blocked on the commercially available VPN services every now and again if the IP address of the VPN service gets flagged as being a VPN - this is usually obvious to the BBC etc. if they're getting a lot of traffic from that specific IP! Your own personal VPN solves this as it's just as if you're using your connection at home, and is specific to you.
There's a really nice guide here -
How to Create a VPN Server With Raspberry Pi
It also includes links to how you get started with setting the Pi up in the first place.
I'd recommend a Raspberry Pi 3 B (or the newest v4) for this. The Spanish distributor of them has a kit available with all the bits -
Raspberry Pi 4 España - Distribuidor Autorizado (the UK distributor is thepihut.com)
Once you had the VPN set up in the UK so you can access it from Spain, you could then choose to add the Freeview TV tuner to it if you wanted as a bonus. You'd then access this through the VPN and be able to stream the TV channels as received in the UK via it.
You could of course do the same thing with an old PC but that would be more involved (installation instructions specific to the PC to get things set-up).
