I thought Jeremy Clarkson and "Top Gear" already proved that going by car is faster than flying
That stupid programme was so blatently rigged it was a total joke.
Any IFR tourer capable of making the distance in one leg would have beaten the car by a factor of about two times, and that assumes perfect driving conditions.
On top of that, that trip (approx Cannes to SE UK, IIRC) was a really good example of a plane being very effective. You have the cross channel hassle with the car (driving to/from Dover etc).
Only a hardened pilot would pretend that for example UK to Crete is convenient or cost effective - unless one can do it in one leg and fast i.e. a TBM700/850 / King Air etc and one has the huge funding (~£500-£700 per hour). The Meridian turboprop is no good because it would need to refuel twice (say, Switzerland, and again in Corfu if not sooner) which means nobody would buy one for that mission if doing it regularly.
Similarly, flights within the southern UK are not justifiable on utility terms unless one is going between say Lydd and St Mawgan, both of which are awful to get to on the surface. But S. UK to Scotland is something else.
What makes or breaks the intra-UK transport case is a proximity (or not) of the airport to where you want to go. This is what gives GA in the USA the massive advantage - most towns have a nearby runway which is maintained by the town, like roads and pavements are maintained here.
I generally don't fly to any place to which I can drive faster. That policy keeps the trips more interesting, and I think this is a mistake many new PPLs make - they stick to the familiar area and before they know it, they have got fed up with the whole business.