"We may even have a little bit of excess (biodiesel) capacity we can sell into the market," he told Reuters.

McDonald's launched its rollout on Monday with half of its 45-strong fleet based in Basingstoke in southern England and in about 12 months would convert all its 155 delivery trucks to run on the green fuel.

Howe said the fuel would not smell of the company's food.

"If our trucks drove around the High Street and it smelt of our fries, what a Pavlovian effect, it would be fantastic but unfortunately it does not," he said.

"It would have been one of the best marketing campaigns we could ever have had," he added.

The biodiesel will initially be made up of 85 percent used cooking oil collected from around 900 McDonald's restaurants and 15 percent from pure rapeseed oil.

"As we get better at the refinement we will be able to remove virgin rape (oil) from the process," Howe said.

Howe said the company keeps its used cooking oil apart from other supplies.

HEALTHIER OILS

"We have ensured we don't have any other oils. A lot of other cooking oils that are collected are very contaminated," he said, noting animal fats can cause refining difficulties.

McDonald's UK is using a mixture of high oleic UK rapeseed oil and sunflower oil from Spain to fry its food. The company switched to the formula in April as part of its strategy to stop using hydrogenated fats.

Hydrogenation can lead to the creation of trans fats which may have worse effects on the human body than saturated fats, according to Britain's Food Standards Agency.

High oleic oils are designed to replicate the stability and long shelf life of hydrogenated oils without the adverse health impacts.

Howe said the company had been using all UK-grown rapeseed oil prior to the switch but now had to rely partly on imported sunflower oil supplies.

British farmers have begun to plant high oleic varieties of rapeseed but supplies are still very tight with imported high oleic sunflower oil much more readily available.

"We are pretty much buying the whole (UK) crop. Our goal is to get to 100 percent high oleic rape," he said, adding McDonald's is encouraging UK farmers to grow more high oleic rapeseed.

Seed companies have expressed concerns that the growth of demand for rapeseed oil from the biofuels sector was hampering the expansion of healthier but sometimes lower yielding high oleic varieties.

By using the fuel, McDonald's will save 1,675 tonnes of carbon per year, the company said.