The shadow defence secretary, James Cartlidge, will say the system is "one of Britain's most significant military programmes since the cold war" and is needed to protect against potential aerial attacks. The proposal includes new advanced radar systems, command and control infrastructure, and a stockpile of interceptor missiles and counter-drone capabilities.
The Conservatives aim to deliver a minimum deployable capability within the first five years, with further improvements over the following five years. The plan would be funded from the party's earlier pledge to raise defence spending by more than £10bn a year to reach 3% of GDP by 2030.
However, the proposal marks a departure from the UK's traditional military stance, which has relied on nuclear deterrence and NATO support rather than standalone air defence systems. Military officials have argued that the UK does not face the same drone and missile threats as Israel or Ukraine, and that any conflict threatening the homeland would involve NATO allies. The UK currently owns no Patriot air defence systems and would depend on Royal Navy destroyers for coastal protection in a crisis.
The Conservative leader, Kemi Badenoch, criticised the Labour government for failing to keep the country safe. The chancellor, John Healey, is expected to delay setting a 3% GDP defence target until next year's spending review.
Other European countries, including Germany, Greece, Cyprus and Poland, are investing in air defence, but the UK faces limited direct threat. The Conservatives argue the UK is falling behind, citing a defence select committee report last November that criticised current investment.