//I can drive to Glasgow, even in moderate to thick traffic, in 4h30mn.//
Where from, Carlisle? :-)
Everybody's needs are different. If I had to go to Glasgow (perish the thought) I can get there in under three hours, entirely by public transport (bus and air from London City). Airport check in is 15 mins, flight time 1h 20m. At least six flights a day. Fifteen minutes from Glasgow airport to the City Centre. If I went by road it's 435 miles. That means at least eight hours (without a stop). In three hours I'd be lucky to have reached Milton Keynes on most days. Domestic airlines provide a useful service for many people.
I don't know anybody who has been deterred from flying by Air Passenger Duty. I fly long haul and pay a ludicrous sum in APD but I've never given a thought to changing my plans because of it any more than I would change them if anybody attempted to "flight sham" me as many gullible Swedes are succumbing to. I feel no shame undertaking a perfectly legitimate activity. The notion that APD "helps the planet" is laughable. All it amounts to is yet another way to pile guilt on to people who are simply going about their business and pleasure and it will do less than nothing to address whatever problem is thought to exist.
That said, Flybe has a cheek in wanting the government to allow them to delay paying their APD bill. They have taken fares from passengers, part of which is APD. The passengers have paid their tax up front (as they are obliged to do) but now Flybe want to hold on to that cash to spend on something else. It's no different to an employer deducting income tax and NI from its employees and then declining to pay it to the Exchequer.