Has anyone had to renew their passport whilst here in Oman?

The British Embassy do not renew passports or issue them anymore; it is done centrally in Dusseldorf now. The turnaround is about 4-6 weeks which isn't bad I suppose. The issue I have is that I was born outside of the UK and it says I need to give evidence of my parents marriage along with my own birth certificate. I can't remember doing this last time? I'm in my thirties...when do you stop showing proof of your parents' marriage???!