Ofgem has opened investigations into British Gas, E.On and Npower over their roll-out of advanced electricity meters to business customers.
Under a government scheme, which began in 2009, electricity suppliers had to take “all reasonable steps” to fit 155,000 business customers with the more accurate meters by April this year.
Now the regulator said it will investigate whether the three suppliers met their obligations after finding they had the lowest completion rates, accounting for more than half of the 40,000 electricity meters still waiting to be installed.
Rachel Fletcher, senior partner for Ofgem's markets division, said: "We are disappointed in the overall performance of the majority of suppliers concerning the roll-out of advanced meters to business customers.
"These new meters offer real benefits to customers including saving money through reduced energy consumption and ending estimated billing.
"Regulatory and government programmes are not optional and failure to meet these in a timely way causes consumer harm. All suppliers can and must learn the lessons from the roll-out of meters for business customers and apply them to the domestic smart meter roll-out."
Ofgem said its assessments found the roll-out was only 75 per cent complete in electricity, compared with 86 per cent in gas. A number of other suppliers did not roll out the new meters to all eligible customers, according to the regulator, and it said it would keep the possibility of action against them under review.
The government has estimated that businesses will save around £40m a year by using the meters, which are designed to offer better and timelier information about energy consumption. Ofgem said it monitored suppliers' progress throughout the roll-out and repeatedly reinforced the need to deliver on time.
A British Gas spokesman said: "British Gas is a committed advocate of smart and advanced metering. Since 2008 we've made significant efforts to ensure that all our business customers can benefit from advanced metering, which will put them even more in control of their energy consumption and help them keep their bills down.
"We remain very aware of our obligations and will continue to work hard to overcome obstacles to the roll-out of this technology. We'll co-operate fully with the Ofgem investigation."