I'm in hucknall (not far from you) have o Rings and a pressure tester if you want me to have a look at it, alas iirc nt11 are renowned for having issues :-(
I have it firing now, I wound the reg in all the way and backed it out about 5 turns and that's got it firing, not only that but it's stopped the leak which is what I hoped for
I live in Watnall so I'm literally round the corner lol