You can apply for a renewal online, mine runs out in June so I have filled all details in online, then apparently the completed form comes back to you by post for you to then return back to passport office enclosing a photo and fees due. Dont know whether that helps though if you are living in Tenerife? Forgotten the website, but I just put Uk passport in Google.

Hi apollo,you can only apply on line if you are on British soil. As you know, there is a British Consulate in Santa Cruz de Tenerife..phone nos.are 922 286863 or 922 286653. Address is Plaza Weyler
Numero 8
st cruz de Tenerife
If you contact them,they will tell you that you can download the form required from the website http://www.Ukinspain.com Click on Passport Applications and it'll be a C1 form you require for an adult application.
Hope this helps!

But beware you have to post it off to Madrid and you know what the Canarian corres (post) service is like!

A bit like the service back home! Yip,allow PLENTY time.

Mucho Gracias all. I shall get onto that today, Im sure I will still be waiting for it this time next year, lol. As Makum said, the correos is slower than a person with no legs on a pedalo.