James Dyson spent years fighting Hoover. Now he intends to clean up

Bagless dust collection, centrifugal technology, cyclonic technology, Dual Cyclone, Triple Vortex - these were the words that rang round Court 58 of the Royal Courts of Justice yesterday in one of the most bitterly fought patent battles of recent years.

Bagless dust collection, centrifugal technology, cyclonic technology, Dual Cyclone, Triple Vortex - these were the words that rang round Court 58 of the Royal Courts of Justice yesterday in one of the most bitterly fought patent battles of recent years.

It was a battle between a multinational corporation and an inventor who struggled for years to find a backer for his ideas, and, when he finally succeeded, saw the firm that had once shunned him and his technology produce a machine similar to his own. Ostensibly about vacuum cleaners, Dyson v Hoover was a battle over the ownership of ideas.

Yesterday, James Dyson, 53, inventor of the bagless vacuum, emerged as victor when the court ruled that Hoover - the company whose name for many has become synonymous with the domestic chore - infringed a patent of Dyson Appliances.

"I spent 20 years developing the technology and I am very pleased to see Hoover, who made a lot of false claims about their product, now found guilty of patent infringement," Mr Dyson said yesterday, after the court ruled in his favour.

"I am also pleased on behalf of other small businesses and inventors who should be encouraged to take out patents by the result of this case. It is wrong to be seen to be able to copy other people's inventions, and this case shows that this can be stopped."

At the centre of the dispute was the Dual Cyclone - a bagless cleaner that operates by using centrifugal force to separate dirt from air. Based on an idea that Mr Dyson originally came up with in 1979, the cleaner was chosen as one of the Design Council's "products of the millennium".

The Dyson empire is now worth around £530m and workers at the Malmesbury factory in Wiltshire assemble about 10,000 cleaners every day. The company has just invested a further £13m in the plant, which employs 1,800 staff.

But it was not always so. When Mr Dyson first came up with the idea of the bagless vacuum no one was interested. Using his Georgian house near Bath as security he took out a loan and hawked his idea around manufacturers including Philips, Black and Decker and Hoover. "Hoover would only see me if I signed an unfair confidentiality agreement, Mr Dyson said. "Electrolux turned it down twice after two good looks at it. They must make millions a year selling bags."

In the end, Mr Dyson borrowed £600,000 to set up his own company and, 5,000 prototypes later, started producing the cleaners himself. Although he patented the idea in June 1980, the product was not launched until 1993. "I struggled over many years to develop this idea," he said. "It was not something that happened in a flash."

The villain of the piece, the object of Mr Dyson's venom, and, as of yesterday, the vanquished vacuum cleaner, is the Hoover Triple Vortex. Using the same idea, Hoover developed its own bagless cleaner which operates using centrifugal force. It was this product that Mr Dyson claimed - during a seven-day hearing in July - infringed his copyright. The court was told that Mr Dyson's invention "turned the industry on its head".

David Kitchen QC, for Dyson, told the court that the Hoover Triple Vortex "clearly" used the same cyclonic technology that had been patented by his client.

Hoover disagreed. It argued that the Dyson design was not unique and that the technology behind the Dual Cyclone involved nothing that was not generally known within the industry. The company denied infringement and attacked the validity of the patent by a counterclaim for its revocation on the grounds of lack of novelty, obviousness and insufficiency.

But in a ruling delivered yesterday in Mr Dyson's absence, Deputy High Court Judge Michael Fysh QC sided with the Wiltshire company. Hoover now faces another hearing on 13 October, when Dyson will apply for an injunction barring further sales of the Triple Vortex. It will also seek damages which could run into millions of pounds.

Judge Fysh's ruling described Mr Dyson's struggle to bring his patent to commercial realisation as "a personal odyssey which makes fluent reading". It went on: "Mr Dyson appears to be a man of practical ability, persistence and business acumen."

Hoover indicated it would be applying to take the case to the Court of Appeal, and would present evidence "not available when the case was heard in July". It claimed that it licensed its technology from BHR Group, a British company specialising in separation technology, notably for the oil and gas industry. BHR Group declined to comment yesterday, though it is understood that Hoover's appeal will rest onthe award of a patent to BHR.

Alberto Bertali, managing director for Hoover in Europe, was "disappointed" by the decision but said the company was already developing a new hybrid technology using a single cyclone (which will not be affected by Mr Dyson's patent) and a strong artificial bag.

But the enmity between the two sides still runs deep. "License the Dyson patent? We have never thought about it," said Mr Bertali at the High Court yesterday.

"License it to Hoover? Not after spending 18 months and half a million pounds in legal costs," snorted Mr Dyson. "They had 20 years when they could have done that."