This might help. It is so easy and quick, do make sure your passport pics are the right size they are very fussy about these now.
http://www.expatwoman.com/forum/messages.aspx?TopicID=138257
Hi there, we just got all ours renewed, and there is a very helpful website which is www.ukinuae.fco.gov.uk
and tells you everything you need to know about sending off your passports to Dusseldorf. If you use DHL (kiosks in several malls across Dubai) you get a special rate of 100 dhs, but everything is on the website about the procedure and costs, and time scale. We got ours back in 3 weeks, all very smooth.
I thought all UK passports had to go to Dusseldorf now to be renewed. MY DH did his about a month ago. It was very quick and came back within 8 days. Not sure about DDs though