Important: If you're renewing abroad please also note that the FAQ section on some of the British embassy websites abroad (I'm thinking Greece here) clearly states that you do NOT need to have your application countersigned if you are just renewing and your appearance hasn't significantly changed, BUT YOU DO. My friend arrived in Athens without a countersigned application and could not get his passport. He had to make another trip the following week at a cost of 150 euro! VERY expensive passport indeed. Countersigning can be a problem abroad because there is obviously less liklehood of people having known you personally for the several years required.
I raised this with the embassy and they totally deny that such advice is given on their website. I then sent them a printed copy of the page and they didn't reply. The errornous advice is still there 6 months later!
Me? I posted my passport to a freind in the UK, had him post it off to Livepool and then he returned the new one to me 10 days later. All done at the standard UK cost. Which is still a rip off.