<<HD, would you be happy with a non comm aircraft turning back and making his own approach path to LHR through a busy TMA in IMC ? >>
I certainly would not be unhappy and have seen a few such incidents. In the UK we have very good radar cover so it's fairly easy to see what is happening and provide the necessary separation with other traffic; it's no big deal. On a 10-hour sector, which was mentioned in the original question, I wouldn't be happy if I was the pilot knowing that I might be out of radar cover for many hours.