Do i need to renew my passport?

Who knows what the future holds.

Personally I would renew it as you never know when you might need one.

Yes.

You can't go anywhere outside of Spain without it.

Although with a TIE you can travel anywhere within the EU - while it (the EU) still exists anyway....

I have had "residency" all over the world (I was some sort of "tour guide")..... It was important to me to have a legal document to show at the passport controls. 

I think it is very important to have a document that shows that you are "alive".

If this thought makes sence?

I would agree with the rest - yes renew your passport. The number of times we have been asked for our passport is unbelievable and we have residencia.

Try opening a Spanish bank account without one.....and if you renew always remember to give your bank a copy of the new one amd update any information stored about your data on airline sites.

Thanks all for the comments and opinions, all valid in their own way.

However i am still trying to find out if there is any legal reason to have one?

Paddy

I don't know the answer but these guys should!

British Embassy in Spain - British Consulate (british-consulate.org) 

Of course you do! You may have Spanish residency but you are still a British citizen. It is illegal for a non-Spanish citizen to live in the country without the appropriate documents from his/her own country.