British Gas has denied claims it paid its staff bonuses to inflate customers' bills.
A former employee told the Daily Mail the policy encouraged staff to target charities and small businesses, with workers told they could triple their salary through commission if they sold enough of the most expensive deals as possible.
The whistleblower claimed the energy giant would sign up churches and charities to the highest-priced tariffs in order to boost their own earnings.
"People were desperate to make the salaries they had been promised, so everyone inflated the prices" he told the paper.
"Scouts was a favourite one; churches, charities, small businesses, where people would just go for the maximum 5p notch-up."
A British Gas spokeswoman said: "British Gas strongly refutes any suggestion that employees are paid commission on any prices charged to residential customers.
"We also reject any suggestion that business contracts have been negotiated inappropriately in our business division, British Gas Business .
"This is a highly regulated and competitive market, and every part of the sales negotiation process for business customers is closely monitored. The contract is always finalised with the clear and explicit agreement of the customer.
Earlier this month British Gas was ordered to pay £5.6 million in compensation and fines for blocking businesses from switching suppliers and failing to tell others their contracts were ending, by energy regulator Ofgem.