Hi Batlet.....We had very much a similar run with Persimmons in Melksham, Wiltshire. Halfway through the build, when we were really looking forward to the moving in day, to our horror we saw the documentary on TV about new builds and were dismayed that Persimmon were one of the 'baddies'.
After seeing this, we instructed an independant surveyor to visit the property straightaway and then at intervals throughout the build stages. Fortunately, he managed to get onto the premises despite Persimmon's greta reluctance to admit him!
Thankfully, he caneback and said that apart from a few minor issues, the basic construction of the house was sound.
That said, two years down the road, Persimmon are still vsiting sorting out issues with our house!!! However, from what I can guage, certainly where we live, Persimmon seem to be the best house builder....you should see some of the houses in the development next to us...it beggars belief to see what they have done yet people still buy these houses.
We had a total of 85 defects, but these were all minor and we didn't have as much trouble as you have, by the sound of it. I hope you manage to get everything sorted but don't let them get away with half a job. Good luck.