The recent cold snap has thrown into focus the varying quality standards of biodiesel and the issues of running fleets on high levels of the eco fuel.

The use of biodiesel is growing a fleets look for cheaper and greener alternatives to traditional fuels.

But not all is going as expected: for example, a bus company in Norfolk had to apologise to customers for “unprecedented disruption” to its services after the biodiesel in all of it 11 buses froze, rendering the vehicles unusable.

First Eastern Counties managing director Peter Iddon said until the problems of using the biodiesel in cold weather are overcome, the bus company will go back to using low-sulphur diesel.

The case illustrates the varying standards of biodiesel, and the differing behaviour of the recycled materials in them in cold weather conditions.

Generally, biodiesel has a slightly higher freezing point than standard diesel.

But, according to the quality of the biodiesel, that freezing point changes.

According to experts at Gloucestershire-based biodiesel producer Green Fuels, biodiesel made from vegetable oil behaves very similarly to standard diesel, freezing at around -12 degrees.

However, the spokesman said those blends made from ‘tropical oils’ such as palm oil, or fuel made from animal fat struggle in the northern European climate, with a freezing point much nearer to zero degrees.

But due to the number of different production methods, there are no standards for production of biodiesel.

Only expensive high-end rapeseed oil based biodiesel has a set European standard - EN 14214.

“Fleets have to pay a lot of attention to the process of making biodiesel, and ensure they are using a supplier who has diligence and understands the process” the spokesman said.

But fleets running their cars or vans of blends of up to 5% biodiesel mixed with normal diesel have nothing to worry about.

Fleet consultant Stewart Whyte said: “The issue with bunkered fuel with 60-100% biodiesel in it is that it tends not to have the additives or anti-waxing agents you get in standard diesel and so is likely to wax at higher temperatures.

“Fleets that are encouraging their drivers to use diesel with blends of around 5% biodiesel in them should have nothing to fear from this issue though.”