A fuel leak which damaged a South Lakeland beck and endangered water supplies to 250,000 homes in Greater Manchester has cost a plant hire company almost 9,000.

Ashtead Plant Hire, from Surrey, pleaded guilty at South Lakes Magistrates Court to Environment Agency charges of causing polluting matter to enter Sillfield Beck, near Gatebeck, after the diesel-powered generator it supplied to run a telecommunications mast was stolen on December 16, 2002.

The mast and compound beside the M6 belong to telecommunications giant, Hutchinson 3G UK Ltd, trading as 3, but Ashtead accepted it was responsible for the security of the generator.

An unknown amount of red diesel escaped from a 2,000-litre fuel tank when thieves broke into the compound and stole the generator, damaging the non-return valves designed to prevent fuel escaping.

EA officers took measures to protect the environment after the spill and Ashtead and 3G spent thousands on a clean-up operation to remove diesel and tonnes of contaminated soil.

EA prosecutor Mark Harris told the court how a drainage ditch leading to Sillfield Beck was heavily contaminated with diesel after the spill and that the fuel had reached the controlled waters of the beck damaging ecology downstream of the discharge.

The leaked diesel also came within metres of Beehive Well which is part of the Thirlmere Aqueduct. The aqueduct supplies ten per cent of the North West region's drinking water and Mr Harris said the incident had presented a serious risk of contamination to the drinking water supplies of up to 250,000 households in the region.

In mitigation, Ashtead argued that it had no previous convictions for pollution in spite of handling around 750,000 litres of fuel a month at hundreds of installations. Counsel Mr Ayers said that the company had taken security measures but the leak had resulted from the actions of serious, determined and organised criminals.

"Security measures were in place in December - they were not impregnable to the determined thief, but what measures are? Is there any such thing as thief-proof security?" he asked.

He also said that actual damage caused by the incident had been slight and temporary.

The maximum fine for this type of offence is 20,000, but District Judge George Wallis said: "Fortunately no harm to humans resulted and no serious harm to the environment was done, but the risks are something that certainly must be considered."

He fined the company 5,000 and ordered it to pay a 3,724.57 contribution towards the costs of the Environment Agency investigation and prosecution.

l Site owners Hutchinson 3G face the same charge in relation to the incident but the company had pleaded not guilty at a separate hearing. Judge Wallis also heard the EA prosecution case in that trial last week, but proceedings were adjourned and 3G will not present its defence until late January next year.