Claydon. I was in the same position a few weeks ago. I called the help line (0300 222 0000) (find your nearest office here
Directgov: Maps - Identity and Passport Service (IPS) Customer Service Centres) and got an appointment the next day. Turned up on time, was seen within 5 minutes of my appointment, took 5 minutes, paid on the way out. My new passport was ready 4 hours later! It cost a bit more than usual (£120-£130 ish) but was worth every penny. As it was a renewal I didn't need a countersignature, just some more passport pics (photo machine on site at the London office). Not much is impressive about most G'ment Depts. but they do passport renewals very well. PS. I did it this way for speed and because I needed my passport and couldn't have it (getting lost) in the post for a week/2 weeks - this was ideal.