Agree 100% TankerTrashNav, I was lucky and had a good run with absolutely no stops or delays, I would normally allow closer to five hours. As you rightly say the trouble with a flight Newquay to Heathrow is that after driving to NQY, parking,checking in, collecting bags at LHR, probably changing terminals it is going to take over three hours anyway and probably cost a vast amount more.
The fares would have to be very competitive and who would be prepared to offer that?
Relevant to Newquay I just flew Vancouver to Nanaimo, around 15 minutes on an Otter seaplane for a shade over £30, what is the equivalent NQY/ISC rate today..... I suspect a lot more!!