Well, that's always a good question
HM Treasury does often seem like a Government within a Government. That said, if a flagship policy was being damaged by Treasury intransigence, I would expect the PM's people to smack a few Treasury heads together. This is a Government that appears to need good news stories.
Price rises can reduce revenue if you price enough people off, price cuts can increase it if you attract enough.
As I've said previously, Governments have been willing to lose revenue for transport benefits.