If you want to send and receive mail to and from the UK, then may I suggest that you try Offex Spain, if you have an Offex in your area.
We use Offex Marbella, and they deliver your mail to an Offex point, which is usually a business in the area such as a Greeting Card shop for example, that offers the extra service as an Offex point.
We address our mail to the UK as normal and drop it off at the Offex point and pay for delivery (no stamp needed as they do that).
When people send us mail, they send it via a P.O Box address at Gatwick Airport, which is then delivered to our local Offex point for collection and we pay a small fee when we pick it up.
Our mail is delivered to the UK, or delivered here from the UK, within 3 to 5 working days!
You can also send Special Delivery items to and from the UK, and also parcels.
I can categorically say that we have never had post go missing whilst using their services.