Northumberland farmers are angry after being told by the taxman their assistance at a historic agricultural show was breaking the law.

Farmers have helped to set up the Glendale Show near Wooler, Northumberland, for decades but this year officials from HM Revenue and Customs told them not to use red diesel in their tractors as the lower-taxed fuel can only be used for agricultural purposes.

Show secretary Sarah Nelson said she could not understand how HMRC had arrived at its decision as the show was explicitly for the benefit of the agricultural community.

“We use local farmers on tractors to move equipment but the amount of red diesel involved is a drop in the ocean compared to people who are knowingly doing it illegally,” she said.

The 115-year-old show was targeted last year when HMRC inspectors arrived to check whether tractors at the show were using standard white diesel – or red.

A tractor was seized and its owner warned that fuelling the tractor with red diesel for non-agricultural use was illegal.

Mrs Nelson said that organisers of this year’s show, which takes place on Bank Holiday Monday, had had to borrow a tractor and fill it with standard diesel.

An HMRC spokeswoman said: “The rebated oil scheme is specifically to support the production of food in the agricultural and horticultural industry and tractors used for non-agricultural purposes do not qualify.

“An agricultural show is not an agricultural enterprise as such, but a profit-making business outside the scheme.”

Show organiser Stewart Nelson retorted: “I can’t believe agricultural shows have been branded “not beneficial to agriculture” by the law.

“I would say that everything we do as an agricultural society in preparation for our agricultural show does have a tangible or direct link to agriculture.”