Just been through the (expensive) process, if you need too as well suggest you start here
http://ukinspain.fco.gov.uk/en/help-for … pply/spain
I used a local courier company to get the papers to Madrid which also checked the forms (they found a small problem, so it was worth their fee, as it saved having it rejected in Madrid)
The new passport has a chip and so can be used in machines at airports which might save queuing at border control.
The new one arrived in around 3-4 weeks, but guess it is their quiet time now.