I finally got around to getting a second passport a couple of weeks ago. I needed it fairly sharpish, so had to go to Peterborough in person. Paid £123 for the one-week service. My interview was on the Friday afternoon, and the new passport arrived on the following Tuesday.
No hassle, no fuss.
The guy doing the application did say that I'd need to send a letter with each passport renewal explaining the need for me continuing to hold a second passport, though.
There's a good template letter on this discussion:
http://http://www.businesstraveller....nd-uk-passport which worked for me.