Businesses that leave lights on in their places of work when no one is present are increasing the cost of their energy bills by almost a fifth, according to an expert.
Penney Poyzer, who appears on BBC2 show No Waste Like Home, added that IT equipment including office computers accounts for around ten per cent of the UK's total energy costs.
The environmentalist added that there are other ways in which business energy customers can reduce both their electricity bills and carbon footprint.
She explained: "Things like water coolers and vending machines - at the weekend these things don't need to be on."
The expert added that by using timer switches, businesses can ensure certain devices are off and helping them save "a lot of C02 and energy".
Recent research by the Carbon Trust emphasised the benefits available to companies looking to become more energy efficient.
The body's study found that if a firm reduced its energy use by 20 per cent, it could add the same amount to its profits as a five per cent increase in sales.
Click here to run an energy price comparison, and see if you could be paying less for your gas and electricity.