Am going through similar situation via a broker and had a DD returned recently and broker has been told and informed me that you have to have clear 6 months of no missed payments/unreturns etc as this is a sign of not being able to manage your finances.
I am going through a mortgage application at the moment and havent a clear credit history. had an credit card about five years ago and missed payments while away in oz, it was subsequenlty cleared and cancelled. I have told the bank all this and they are of the opion that it shouldnt affect my application. either way i will know in about two days time. I always thought i had no chance but my bank seem quite positive so i think everyone should apply themselves and just see. No harm in trying.