That's down to the fact that there hasn't been anything more than maintenance investment in the english transport system since the 70's. It's probably the most over-priced, ineffective train system in the whole of europe. Partly because when it got privatized, most of the buyers were national train companies from other european states - who use the british train system to subsidize their own trains.
But the journey from Cambridge train station to Coventry train station takes 1h47m by car and 2h16m by train [1], as the train takes a V shaped route via London. Birmingham New Street station to Norwich station takes 3h6m by car, 3h57m by public transport [2]. Kings Lynn to Cromer, 1h7m by car, 2h27m by public transit [3].
And that's going from train station door to train station door in major cities - if you're going to somewhere out-of-town, the public transport penalty can be even greater.
Doesn't mean we shouldn't build public transport, of course. I'm not a car owner, so I rely on public transport to get around. But we also shouldn't deny the downsides of public transport.
[1] https://www.google.co.uk/maps/dir/Cambridge+Station+[CBG],+S... [2] https://www.google.co.uk/maps/dir/Birmingham+New+Street+Stat... [3] https://www.google.co.uk/maps/dir/kings+lynn+train+station,+...