Ofcom’s rules were brought in to protect consumers and stop unexpected price rises occurring in the middle of a contract.
They stated companies had to tell customers how much their bill would rise by “in pounds and pence” before they signed up.
At the time, Ofcom’s director for networks and communication, Natalie Black CBE, said: “Our new rules mean there will be no nasty surprises, and customers will know how much they will be paying and when, through clear labelling.”
But the rules only banned price hikes linked to inflation.
O2’s price increase is a flat fee rather than a percentage of the monthly bill.
Telecoms analyst Paolo Pescatore of PP Foresight said “O2 is pushing the boundaries” of the regulation.
“This is extremely unfortunate, given that the mobile operator should be focused on retaining customers in a cut-throat market,” he’d told BBC News.
Meanwhile Tom MacInnes, director of policy at Citizens Advice, said it showed Ofcom’s actions “haven’t gone far enough”.
“The regulator needs to wake up and make these essential markets work for everyone,” he said.
“Ofcom needs to go back to the drawing board and bring forward plans to stamp out mid-contract price rises once and for all.”
Mr Lewis also said he had written a letter about this addressed to the chancellor, the technology secretary and the head of Ofcom.
BBC News has contacted them for comment.
Ofcom did not comment on Mr Lewis’ letter.
Ernest Doku, telecoms expert at Uswitch, said while the regulator’s latest telecoms complaints figures, external were “at some of the lowest levels ever”, service issues were still the main driver of complaints about mobile and broadband providers.
“Against the backdrop of increasing annual price rises, providers need to recognise their responsibility to deliver corresponding improvements in service and value,” he said.
“For consumers, this data is a timely reminder to compare deals regularly and switch if their provider isn’t sufficiently meeting their needs.”