Consumers have been warned that green energy could be the next big mis-selling scandal, as door-to-door sales sharks push energy-saving products that could lead to bigger bills.

The government is offering tax breaks on fuel-efficient cars and homes, but some firms are using the green agenda to con people out of thousands of pounds.

Ofgem, the energy regulator, and Energywatch, the independent watchdog, expressed concern about mis-selling last week.

“Consumers should be aware that people will try to exploit the green agenda and we expect mis-selling to be more common in the future,” said Energywatch.

Consumer Direct, a free government-backed advisory service, said it had received more than 1,000 complaints from consumers last year claiming they had been mis-sold solar thermal products that heat water and are supposed to cut consumption and therefore your energy bill.

Sunday Times reader Dennis Robinson, 73, who lives with his wife, Maureen, 74, in Lancashire, was sold thermal solar panels for £6,000 by the Dorset firm Simplee Solar. Robinson says he was advised that his total energy bill would be cut by between 30 per cent to 50 per cent.

However, he is now paying 30 per cent more for his energy than before installation, and he has been told it could take up to 60 years to pay for the solar panels with savings from lower energy consumption.

Last November Simplee Solar was fined £40,000 by Bournemouth Crown Court for distributing flyers claiming its heating panels could cut fuel bills by 70 per cent.

Dennis Robinson was first approached by a Simplee Solar salesman in December 2005.

“I remember him telling us that we could save between a third and a half of our overall energy bills – not just our water bills,” said Robinson. In fact, solar panels generally cut water-heating bills by a third, but this translates into about 5.5 per cent of an overall bill.

At the time, the Robinsons were on Powergen’s Staywarm tariff, which charges a fixed annual rate to protect customers from fluctuations in wholesale energy costs.

They were paying £972 for both their electricity and gas for the year ending in April 2006.

After the installation, the couple were allegedly advised by a Simplee Solar manager to switch to EDF Energy to enjoy the benefits of their solar panels.

EDF agreed to charge them a direct debit of £46 a month, cutting their bills to £522.

By December 2006, however, their annual bill had gone up to £960 – only £12 less than what they were paying with Stay-warm.

And last month their bill went up to £1,280 – a 34 per cent increase on their bills before the solar panels were installed and almost 60% more than they were originally quoted by EDF.

Mr Robinson feels he has been misled both by Simplee Solar and EDF.

“We’ve spent £6,000 to save energy bills, but now we’re paying more than we did. I’m sure EDF will say this is to do with the rise in wholesale energy prices, but I feel I was misled into switching to them with a low initial monthly payment.”

EDF, which said it had no links with Simplee Solar, admitted that the initial monthly payment it quoted was too low.

“The rate of direct debits has had to increase because setting them too low in the first place led to a debit on the account,” EDF said.

Simplee Solar said the Robinsons’ energy increases were due to wholesale prices going up and added that it was impossible to compare the savings made as they had switched suppliers.

Both the salesman who sold the Robinsons their solar panels, and the manager who allegedly advised them to switch to EDF, no longer work at Simplee Solar.

Simplee Solar director Thomas Callaghan denies that any of the firm’s employees recommend savings of up to 50 per cent, although a letter to Mr Robinson from the firm states that up to 30 per cent of a household’s energy bills could be saved with their panels – a more accurate figure would be 5.5 per cent, according to figures from the Energy Saving Trust.

The company also denies that it advises customers to switch energy supplier It does admit, however, that the solar panels should not have been sold to someone on a fixed tariff because they would never have benefited from price falls anyway – had they not switched.

John Walker, a director of the Solar Trade Association (STA) warned about “cowboy” solar panel salesmen.

He said he would “seriously question” any salesman claiming a saving of more than 30 per cent on a household’s total energy bill using thermal solar panels.

“Overselling the benefits of solar power is a problem in the industry,” he said. “It’s simply not true to suggest that you can save a half of your overall energy bills with that kind of system.”

He added that the £6,000 cost of the solar thermal panels was excessive. “A more realistic price is between £3,000 to £4,000,” he said.

Simplee Solar is not a member of the Solar Trade Association. Walker advises people to use one of the 120 approved STA members to fit solar panels. A list can be found on the association’s website.

Trading Standards said the firm had improved since the court case, though people who were sold a Simplee Solar product before the beginning of 2006, when the firm stopped distributing misleading literature, might be able to claim back money at a small claims court. They should first contact the firm and only go to the courts if they cannot resolve the issue.

Other companies attracting complaints include Smart Energy (UK) – where Simplee Solar founder Lee Comer was once a director – Solar Technik, based in Bournemouth, and Spectrum Energy, which is now in liquidation.