Louise Haigh
"Where's she meant to get the money from?"
The PM did not meet the demonstrators or mention them in a speech on Saturday.
"It will backfire on them," a senior government source said.
The whole saga looks "messy," according to Laura Kuenssberg.
Transport secretary Louise Haigh said local councils "would have my full support" if they introduced them in their areas.
Louise Haigh had the perfect quip for everyone who remembers one of the most pivotal political moments of 2014.
The pledge will form a central part of the party's election manifesto.
He has been told to "get back to work" and resolve the long-running pay dispute.
The department for transport's own impact assessment warns the plans could lead to more strikes and staffing shortages.
The shadow transport secretary said putting the network in the hands of private companies had been a "failed experiment".