A Newcastle Evening Chronicle reporter spent a day undercover with customs officers on the trail of motorists who are illegally filling up on red diesel.

Adam Jupp's investigation revealed how the taxman is being cheated out of millions of pounds each year by people using the fuel, some of which can be traced back to criminal organisations, including the IRA.

The illegal use of red diesel – which can be bought for half the price of normal diesel because it has a reduced rate of excise duty – is particularly prevalent in the north east.

Adam told HoldtheFrontPage: "I've done stories with customs officers before – but everyone knows about things like cigarette smuggling, so I wanted to look at an area that they deal with on a daily basis but perhaps people don't realise.

"After a casual chat with customs officers I found out that the north east was a problem area, so when your patch has a problem it makes it all the more newsworthy."

After witnessing the customs officers apprehend three offenders during the day, Adam also got in on the act by spotting a fourth motorist filling up at a garage.

Adam said: "We were driving off from the garage when I spotted another bloke going to fill up a drum so we did a U-turn in the road and went back and caught him."

It is only legal to use red diesel – so called because of the coloured dye added to identify it – in tractors, lawnmowers, snow clearers, gritters, mobile cranes, diggers and other agricultural engines.

In the UK, more than £850m of duty is lost every year due to people using red diesel illegally.

Recent figures showed that the detection rate in the north east is 32 per cent, compared to a national average of six per cent.

An HM Revenue & Customs spokesman told the Evening Chronicle that problems in the region were due to areas of deprivation, with people using the fuel to save money, and the number of farming areas.