It's not much use to you now but it may help others to know that there is a way to speed up passport requests which need to be made at short notice.
The normal postal process needs 3 weeks. The Check and Send service you used aims to get passports back in 2 weeks but they don't guarantee to do it in 2 weeks.
"This service is available through certain Post Office branches. Your application should take two weeks from the time the branch or agent accepts the application, not including bank and public holidays. This is not a guaranteed service and may take longer during busy times. IPS advises you not to book any travel until you have your new passport."
If you need it in less than 2 weeks there is a fast turnaround facility. Personally , given the problems that can occur, I'd use it if I needed it within 3 weeks just to make sure.
There's even a 24 hour turnaround service
http://www.direct.gov.uk/en/TravelAndTransport /Passports/howlongittakesandurgentappplication s/DG_174149
Good luck.