INVENTOR James Dyson has been cautioned over polluting a river near his home in the same week he topped a Sunday Times rich list.

Mr Dyson, 57, was top of the South West section of the list with a personal fortune of £1,050,000,000.

Mr Dyson, who is said not to be interested in rich lists, declined to comment on his wealth but a spokesman said: "We invested £40 million in 2004 in research and development and that level of commitment is paying off. James works every day in the labs. He is an engineer more than a businessman."

Mr Dyson's fortune increased by £250 million in the last year. The spokesman said: "This reflects Dyson success in recent years. We have recently become market leader in the US and last year made record profits. James has not cashed in his chips. His wealth is tied up in Dyson of which he and his family own 100 per cent."

The billionaire however, has fallen foul of the Environment Agency. He has been given a formal caution for allowing silt from ornamental lakes at his £15 million country estate at Dodington, near Chipping Sodbury, to be dumped in the River Frome.

However, legal proceedings were dropped by the Environment Agency on Tuesday at North Avon Magistrates' Court in Yate.

The agency said there was not enough evidence to convict him. Instead Dyson agreed to accept a caution.

At an earlier hearing in February the prosecution claimed the pollution had wrecked spawning grounds for brown trout living in the river.

Environment Agency spokeswoman Bridget Norris said: "We decided to withdraw proceedings as we felt there was not enough evidence to convict him. If he commits another offence however, this case can be taken into account."