Scottish supplier SSE took a covert swipe at its competitors yesterday for “undercharging” internet customers at the expense of others while ostensibly backing the Prime Minister’s announcement that all the suppliers should offer customers their lowest tariff.

This isn’t the first time the supplier has broken ranks with fellow Big Six suppliers over energy policy in the run up to the Energy Bill.

Last month the firm’s Chief Executive Ian Marchant took EDF Energy to task in a newspaper article for its alleged attempts to get a better price for nuclear power, a charge refuted by the French rival.

Yesterday afternoon David Cameron told MPs in the House of Commons laws would be put in place to make sure suppliers must offer the cheapest tariff.

In response the supplier said: “For too long some companies have undercharged, in particular, customers who sign up online, at the expense of those without access to the internet. It is not fair and discourages trust in the market.”

The Scottish energy firm claimed it has “long been campaigning for an intervention by Government to ensure that differential pricing, as undertaken by some of SSE’s competitors, is banned” and it looked forward to more detail on the announcement.

The statement went on: “SSE has just three tariffs available to all customers, whether new or existing and regardless of sales channel. Prices only vary by payment method, if customers choose to fix their tariff, or if customers choose electronic billing. Other suppliers should follow our lead and we hope to work with Government to ensure that this practice is enshrined across the industry.”

A DECC spokesperson could not confirm which body would enforce David Cameron’s policy but told ELN more details would be in the Energy Bill, due in November.

The regulator Ofgem’s Retail Market Review (RMR) which could be released by the end of the week could also shed some light on the issue.