Almost half of the energy used by British business is wasted when employees aren't at work, a report has claimed.
British Gas said that 46% of the electricity used by businesses is consumed out of office hours.
The energy company analysed more than 6,000 smart meters to show that unnecessary uses of electricity accounted for almost half of UK businesses' energy bills.
Unnecessary uses of power found by British Gas included companies lighting car parks on weekends, pubs keeping fruit machines on after hours and vending machines being left switched on in offices.
British Gas also released three nighttime thermal images of business centres in Manchester, Liverpool and London.
The company said that the images, shown in the slideshow below, provide a visual insight into how much energy is being wasted by companies when their employees aren't working.
The energy company's findings echoed a recent report by the Environmental Change Institute (ECI) at Oxford University, which called for all businesses and homes in the UK to be carbon neutral by 2050.
Released in January, the report identified wasteful energy usage as a key area where the UK had to improve in order to meet its climate change targets.
But although it identified some policies that could be implemented to reinforce energy efficiency, the ECI report said that businesses had to realise the economic benefits for themselves.
"These soft-measures, involving naming and shaming, will be most successful when businesses realise the financial benefits that come from lower energy bills, better conditions for the workforce and the enhanced value of their properties," said the report.
Doug Parr, chief scientist at Greenpeace UK who produced the report with the ECI, told the Huffington Post UK:
"It's often said that energy bills are too high, and what we do know is that some of those bills are likely to be too high because energy is being wasted by usage.
"But none of that absolves energy companies and government for not taking the measures that need to be taken on improving buildings, on putting better efficiency regulations in place, working in Europe to get appliances progressively more efficient - all of that still needs to be done."
Greenpeace said that energy was to some extent a controllable cost, and that the more information businesses had about their usage the better it would be for the environment and the bottom line.
But a group representing small business insisted that providers still had to face increased competition.
The Federation of Small Businesses (FSB) called on the government to open up energy markets to enable smaller companies to compete with the 'Big Six'.
John Walker, national chairman for FSB, told the Huffington Post UK: "We welcome any initiatives that will help small businesses drive down their energy costs and smart meters should let small firms see in real time the energy that they are using.
"But, for too long small firms have been at the mercy of the big six energy suppliers; been locked into unfair contract terms and subjected to unfair price increases.
"The biggest single thing that can drive down energy prices is more competition in the market and we want to see the government take action to open up the energy market to new entrants and give small businesses the fair deal they deserve."
The British Gas report was released on the same day that the consumer group Which? along with the activist network 38 Degrees said it was launching a campaign to enable large groups of consumers to bargain for better energy deals and switch en masse, in an effort to pressure companies to lower prices.
Almost 100,000 people have signed a 38 Degrees petition calling for fairer deals on energy.
David Babbs, executive director of 38 Degrees, said: "We're all sick of gas and electricity companies ripping us off. If thousands of customers band together, we'll have the bargaining power to do something about it.
"The big energy companies act like they're untouchable, but this people-powered campaign can turn the tables and bring down prices for everyone."
Energy comparison websites said that businesses could also making savings by searching for a better deal.
John Altamura at UK Power, a price comparison website accredited by the Consumer Focus Confidence Code, told the Huffington Post UK: "Rising energy prices have certainly put a strain on small businesses. However businesses often don't realise that they can save up to 50% on their renewal rates simply by switching to the cheapest deal.
"Our message to these businesses would be to engage more with the energy market, not to let their contracts automatically renew, but to get quotes from multiple suppliers."
British Gas said it was launching a service to help companies identify inefficient uses of energy, and to advise them on how to save money by cutting that waste.
The service, Business Energy Insight, gives companies smart energy meters, access to an online energy-use dashboard and support from British Gas to cut costs.
According to British Gas, businesses already using the new service such as the Authors' Licensing and Collecting Society can save up to £9,000 a year by making small changes to their energy usage.
A spokesperson at the department of Energy and Climate Change (DECC) told the Huffington Post UK:
"UK businesses could save money and cut carbon by improving their energy efficiency.
"The government has introduced the Green Deal through legislation which will help business take advantage of energy efficiency measures such as insulation with no upfront costs.
"This week DECC will be launching the Energy Efficiency Deployment Office to put energy efficiency at the heart of energy policy."