At last night's North East Economic Forum in Newcastle, the speaker, Alex Salmond, was asked if eventual Scottish government control over setting the levels of APD would adversely affect Newcastle Airport by attracting its passengers north.
His response was that Edinburgh and Glasgow Airports wanted to attract passengers from Heathrow, not passengers from Newcastle. Visitor numbers at Edinburgh Castle (a good indicator, apparently) had fallen by 20% during the Olympics as people chose not to visit the UK due to warnings over meltdown at Heathrow. This showed, apparently, the reliance that Scotland had on passengers interlining through Heathrow.
Clearly, should Scottish independence lead to a significant economic upturn north of the border, and a consequent expansion of services and routes from Edinburgh Airport, then growth at Newcastle might be squeezed; however, most commentators - Salmond apart - would class that as highly unlikely. In the meantime, perhaps Newcastle Airport could respond to any perceived 'poaching' by marketing itself as the gateway to southern Scotland?