NEW: Thousands of farmers from across the UK are gathering in central London in the biggest protest yet against the govt's changes to inheritance tax rules. The reforms, will mean farms worth over £1m will be subject to 20% inheritance tax from April 2026. Farmers say that will lead to land being sold to pay the tax bill, impact food security and the future of British farming. The govt insists it is "committed" to the farming industry but has had to make "difficult decisions".