“We put posters up at bus stops as well as cleaning and maintaining bus shelters and it’s quite hard to work at bus stops during the day.”

Ewen explains that as the majority of Clear Channel UK’s sites are in city and town centres, air quality is a prime concern.

The company has an environmental steering committee and has been named in the Sunday Times ‘Best Green Companies’ list for the past four years.

The listing recognises organisations that are making a real difference in their environmental performance.

Clear Channel UK’s environmental manager Martin Page plays a key role in the fleet.

“He produces an LPG report every month which shows which vehicles are not achieving 85% LPG use and how much we could save if they were,” Ewen explains.

Drivers are then contacted to find out if something is wrong with the vehicle.

Ewen admits that LPG vehicles are not problem-free, with the most common issue being the engine management light coming on inexplicably.

“What a lot of people forget is that if there is a problem with the LPG system the vehicle will still run on petrol,” Ewen adds.

“So drivers are still able to carry out their work and book the vehicle in at a convenient time, whereas if a diesel has a fault it won’t run.”

Clear Channel UK has a network of LPG repairers through Nicholson McLaren (the company which carries out its LPG conversions).

The problem Ewen has at the moment is there is a lack of petrol vans of the right size for Clear Channel UK’s needs that can be converted to LPG.

The next best thing would be a petrol hybrid van, although none are available yet.

Ewen intends to trial both an electric car and van but is not convinced electric is right for his fleet.

“It’s not practical for us to use electric vehicles across the country,” he says.

“We’ve got vehicles doing 400 miles a day in some cases so it’s not possible to use electric.

“We’ve got some vehicles doing very little mileage on a daily basis but the issue we’ve got there is they are based at the driver’s home and not at a depot.

"If we were to bring the vehicle back to the depot we could increase their daily mileage by 100 miles. They may not even be able to carry out their daily job because they would have to travel too far to get to the job and back again.”