This is such an interesting question, wow! I know a lot about British Passport, but this question comes up, so rarely, I can't remember with 100% accuracy what the answer is. I would call the Passport office and find out.
Call HM Passport Office in Durhamm UK, it's really a great call centre, and they should know: +44 300 222 0000
Thomas, if you get the answer, please come back and tell us. If you did not get the answer, come back, and I will try looking for someone to help you.