The Archers "tricked" 1950s farmers into adopting modern techniques by portraying small holders as "inefficient and backwards", an adviser to the show has said.

Graham Harvey, who helped write hundreds of episodes of the Radio 4 programme, said small farmers were given a "clown" image because the broadcaster backed a government agenda to bring farming into the 21st Century after the Second World War.

He said the show subtly praised larger farms, despite 70 per cent of the world's food being produced by small-scale farms, and listeners were duped into adopting more up to date practices.

Author and columnist Harvey spoke out at Chalke Valley History Festival near Salisbury - the UK's biggest history festival.