Shadow energy and climate change secretary Caroline Flint accused the UK Government of presiding over a "broken energy market" and said Labour would hand a tough new regulator the capability to cancel energy companies' licences where there were repeated instances of the most "serious and deliberate breaches of their licence conditions which harm the interests of consumers".
Ms Flint is due to visit Reading East and Reading West later today where she will speak on the issue.
Figures obtained under the Freedom of Information Act, she claimed, showed energy companies had continued to "mistreat their customers" and face another 16 probes into mis-selling, poor customer service and other bad practice, despite Ofgem issuing 30 fines, totalling more than £87 million since 2001.
Under Labour's wider reforms to "fix" the energy market, Ms Flint said, the regulator would be charged with producing an annual scorecard for energy suppliers, reporting on the company's performance and identifying areas of concern.
Ms Flint said UK household energy bills have risen faster than almost anywhere else in the developed world since Labour lost office.