The masks were part of a £252 million ($332 million) contract the government signed with investment firm Ayanda Capital in April.
The papers, published Thursday, are part of a lawsuit against the Conservative government by campaigning groups the Good Law Project and EveryDoctor.
They want the courts to review contracts signed by the government for personal protective equipment, which they say were not properly scrutinized.
Jolyon Maugham, director of the Good Law Project, said the government had signed three contracts worth more than 100 million pounds each “with respectively a pest control company, a confectioner and a family hedge fund.”
Keir Starmer, leader of the main opposition Labour Party, called for an urgent investigation into the way personal protective equipment was acquired.
Coronavirus: Boris Govt Decides Masks Work After All https://t.co/Tq5hBU7i77
— Breitbart London (@BreitbartLondon) May 12, 2020