Prime Minister Theresa May stunned the energy market on Wednesday when she announced a plan to impose price caps on standard variable tariffs, the basic rates that energy suppliers charge if a customer does not opt for a specific plan. Around 70 percent of households are on SVTs.

"If they (the regulator) need legal back-up there is a strong consensus in parliament for this, so we will publish legislation and we'll invite the whole house to endorse this so that they have the legal certainty," Clark told BBC Radio 4 on Thursday.

(Reporting by Kate Holton; editing by Estelle Shirbon)