The UK PM emails road pricing signatories, those who signed the petition opposing pricing. His letter is interesting from a number of perspectives, and was clearly written in part by transportation professionals.
However there is an (intentional?) misrepresentation of the induced demand problem hidden in the text.
If it is the "beginning ,not the end of the debate", it has not got off to a good start. There are several elements missing from the context, though perhaps they will be brought back in:
1) Hypothecation (the British term for earmarking) - money raised from transportation should be spent on transportation (or its impacts). When talking about building facilities the PM says "Tackling congestion in this way would also be extremely costly, requiring substantial sums to be diverted from other services such as education and health, or increases in taxes." Implying more money for roads from the same gas tax is less money for something else. This is because in the UK the petrol (gas) tax is used as a cash cow to cross-subsidize other sectors of the economy that should be paid for out of general revenue or otherwise. If people instead saw transportation taxes/tolls/prices as paying for transportation services, there would be more readiness to do so.
2) Local decision making - most travel is local, decision making about tolls and pricing should be local (though obviously there are positive network externalities associated with choosing a common technological framework).