So, just to update...
I had an independent surveyor come to take a look, and they agreed that whilst the crack is due to themral movement and here is nothing too serious going on, the fact that several other properties of the same design have cracked in the same place could indicated a design weakness/issue. He also suggested a more robust method of repair involving some sort of stitching might be more appropriate/necessary. I forwarded my concerns and report into the NHBC who did not reply. I sent them a reminder over a month later and they say they will not reconsider as the policy does not cover themal movement or shrinkage.
I responded that I don't believe this is the sole cause and the report suggests a design flaw-to which he has replied that they don't take other properties into consideration.
This feels like madness and is very frustrating. Should I just give up and face the fact I'm going to get nothing out of them? My opinion of them could not get much lower right now.
