In pictures: Farmers descend on London ahead of budget announcement

The farmers have turned out in a show of strength against the Inheritance Tax changes, which threaten thousands of family farms across the UK

A person attending the protest said farmers were gathering round Trafalgar Square after police stopped tractors from getting into Whitehall.

She said officers have threatened to arrest some drivers and there is gridlock in central London round Trafalgar Square.

She added: “The Police action is contributing to the traffic chaos. It would be better containing them in Whitehall.”