The government would be flying in the face of its own declared aim to maintain an affordable and secure domestic food supply base by upping fuel duty, NFU South West regional director Melanie Hall has warned.

"We are committed to lobbying hard against any further rise in duty," she said.

"We are also deeply concerned about proposed big excise duty hikes for the sort of vehicles used for indispensible day-to-day work on and around farms and are looking for an exemption for them," she said.

Returns for some farmers had recovered somewhat from very low levels, she added, but there remained a huge disparity between sectors and she said the NFU was extremely concerned at the huge rises in their costs which, in many cases, were wiping out any gains.

She said poor returns over a prolonged period had seen farm investment cut savagely and now the big rise in farmers' costs may well mean this trend would not be arrested, keeping food production and national food security in jeopardy, directly contrary to the government's declared intentions. The knock-on consequences of poor farm profit margins for other businesses in the rural community and beyond were bleak, too, she warned.

"Rural areas are particularly vulnerable to exorbitant fuel prices," she said on the opening day of the Bath and West Show, one of the biggest events in the countryside calendar. "With village facilities diminishing, people are heavily dependent on their cars and many need oil-fired heating, too."