A senior adviser to Environment Secretary Michael Gove has called for a review of tax breaks for farmers.
Economist Dieter Helm said the current system led to "subsidy addiction".
Professor Helm, who said he was speaking in a personal capacity, told BBC Radio 4's Today programme: "If you're producing 0.7% of output, receiving £3 billion of subsidies for that output of about £9 billion and being exempted on rates, and being exempted on diesel and being exempted on inheritance tax, this is quite a list and we've got there by accident almost, one after another of these concessions has been made, it's kind of a subsidy addiction in the end.
"Farmers receive not just the £3 billion of subsidy, they receive a whole range of other benefits that nobody else in the economy gets."
National Farmers Union vice president Guy Smith told the BBC that government assistance helped British agriculture stay competitive.
"What we are rightly weary of is having to compete against farmers in other parts of the world who get greater levels of support, or who have different costs of production because of different policy."