I am sure however that a new runway open for SH ops with an easy connection on LH destinations would create a market that would be quickly filled. Not only from the UK regions but also Europe. We would also likely see new routes to destinations that were not previously viable even for Heathrow.
Or easyJet move in and fly people on holiday to the same destinations...
Are the environmental issues really spurious - more flights means more noise, and it ain't cheap.
Talking about the differences in the level of regional infrastructure expenditure isn't just a "fan club" issue.