Whitechapel will supply PowerHouse with its entire car fleet, covering 100 vehicles, allowing staff to receive the equivalent of a company car but without a benefit-in-kind tax burden.
This allows employees to drive vehicles that might have high emissions without the penalties they would otherwise suffer under the new carbon dioxide-based benefit-in-kind tax regime.
The firm has more than 23 stores spread from Inverness to the Isle of Wight, including 168 superstores and 63 high street stores.
Ron Jenkins, human resources director of PowerHouse said: 'Our employees were understandably concerned at the increase in their tax liabilities and we looked at a number of options to counter this. However, we are extremely pleased with the solution Whitechapel developed.
'It retains all the benefits of the traditional company car scheme and removes employees from the potential of a spiralling benefit-in-kind tax burden with the company car.'
As well as expanding the range of cars employees can choose from, they will also be able to specify the length of their contracts, and will be given the option of retaining the car at the end of the contract or handing it back.
Sue Wintrip, Whitechapel business development manager, said: 'We took a consultancy approach in the development of the PowerHouse scheme, seeking input from the company and their employees.
'The recent changes to company car taxation rules have altered the nature of the fleet market. Our car ownership scheme enhances the way vehicle benefits can be delivered, providing PowerHouse with the potential for significant cost savings.'
Whitechapel was established in 1991 and focuses on providing employers with alternative methods of providing employee transport, at a lower cost than the traditional company car.