DODGY power companies are to be investigated in an attempt to rebuild public trust in market competition, the energy regulator announced yesterday.

Ofgem said soaring household bills and intensifying public distrust highlighted the need for an investigation after profits at the Big Six energy firms quadrupled to more than £1 billion in three years.

It added that the Competition and Markets Authority (CMA) probe should ensure “once and for all” that competition works effectively — a task many say is impossible.