Have you tried the HNBC? They should cover your house from building defects for a further 8 years after the builders warranty finishes.
Unfortunately the NHBC warranty is mainly for large scale building defects that occur in years 2 - 10. There is an accumulative excess that applies to all claims that goes up each year, I'm not sure what it is in the earlier years but by the time your at years 8-10 any works you need carried out must come in at more than £1000+ for them to cover it. It's a silly system and in many cases makes the warranty worthless. I'm fairly sure they won't cover anything considered cosmetic either, only structural.
For example, when I moved into my current place it was in year 9 of the warranty. 3 double glazing panels had blown in various windows but the houses first owner had just left them, I contacted NHBC and they told me to get 3 quotes, if it was over £1500 (the excess in year 10) then they would cover. Of course 3 double glazing units cost £300 max (even with the fitters being "liberal" with their costings) so it provided no help.
In cases where a house has been so badly built that something major needs to happen to make the property sound again then the NHBC will be a god send as normal insurance won't cover that kind of thing (that only covers accidental damage or damage caused by something our of your control like major subsidence (policy withstanding) or the weather) but for the usual house niggles, they need to be sorted in years 1 and 2 by battling with the builder and if anything happens after that point, it's down to the home owner to stump up.
EDIT: Beaten to it by the op, sounds like the NHBC warranty is becoming even more worthless as time goes on!
