Johnson left school aged 18 with no formal qualifications, and went to work in Rooksby's butcher's shops in Peckham, owned by John Manson Ltd.
Despite being the son of one of the company's owners, he was shown no favouritism, and left after 3 years to study theology and philosophy with the White Fathers in Ireland with thoughts of becoming a missionary.
Johnson returned to John Manson Ltd in 1966, becoming a trainee meat buyer at Smithfield Market, and then becoming the manager of the company's butcher's shop on the King's Road.
He wanted the company to move away from high street butchery and to concentrate on selling mail order hampers, but his father and the other directors did not agree.
Farepak expanded its mail-order hamper business to include frozen food, drinks, Christmas gifts, and shopping vouchers.
He funded expeditions to Malawi, Ghana and Indonesia by orthopaedic surgeon Hein Raat, and became a funder and trustee of the Impact Foundation which operates hospitals in Africa, India and Bangladesh.
Johnson became a director of (and investor in) Prospect magazine, sponsored Garsington Opera, collected works of art, and advised the Ashmolean Museum and Bodleian Library.