Secret diplomacy by Margaret Thatcher helped land the UK’s biggest arms deal, and prevented the contract for fighter aircraft going to the French, according to newly released files.

Foreign office files released by the National Archives at Kew in West London detail the delicate diplomatic tightrope the Prime Minister walked to secure the sensitive contract, and the efforts made to keep the negotiations under wraps.

Documents show that in April 1985, Mrs Thatcher made a stop over in Saudi Arabia that helped seal the controversial Al-Yamamah deal on her way back from a tour of south-east Asia.