Since Januray tankers have collected nearly 30,000 litres of waste oil from 15 of the chain's 74 restaurants in the Republic, and half of it has been converted to biodesiel by Greyhound Recycling. In Britain 155 tankers collect 24m litres of cooking oil every month after its been used to fry chips and chicken nuggets in 900 restaurants.

The oil is processed through separation tanks where food particles are removed and then transformed into fuel at a biodiesel conversion plant.

McDonald's said the Irish pilot was a demonstration of its commitment to becoming "a good corporate citizen", although there is probably an efficiency rational behind the project too as the company looks to transform a waste product into a cheaper supply chain input.

Mathew Howe, McDonald's UK supply chain manager, said the cost of using reconstituted cooking oil in the British delivery fleet was likely to equal regular diesel costs over the long term. He told reporters the short term costs would exceed diesel prices but only by "a couple of pennies per litre".

The company was unable to confirm whether tankers moving oil from restaurants to a conversion plant would themselves be powered by a biodiesel fuel.

In Britain, the fast food group has been running trucks on a mixture 95% diesel and 5% biodiesel. The new mix will be 85% biodiesel and 15% rape seed oil. The mix will differ in ieland because of separate legal restrictions.

McDonald's has been keen to stress its environmental credentials of late, and since last year has agreed not to use soya beans from newly deforested Amazonian lands as well purchase coffee beans certified by the Rainforest Alliance. UK coffee sales have reportedly by grown by 10% since certification.