IO540:
Many people would disagree with the above (Class G is Class G regardless of who you are talking to) even if it seems perfectly reasonable to me that one should follow ATC instructions since they are usually given for a good reason
I'd venture that it's not just when they're given for a good reason that you should follow them. You should follow them because the ATCO expects that you will follow them and will have developed his plan on that basis. So if you think they're bad instructions you should tell the ATCO straight away that you intend to do something else. That's why you will frequently hear ATCOs saying things like "report if you wish to do X" because they recognise you have the freedom to do that but they want to make sure they're kept in the loop.
NB no suggestion being made here that any of this happened at Coventry last weekend.
NS