Proud founded the Proud-Bailey Company Limited in 1961 through which he published handbooks covering the postal history of over eighty different British colonies and which illustrate more than 50,000 postal markings. Proud-Bailey became a major postal history dealer. He sold the firm to
Stanley Gibbons in March 1987, as a result of which he became joint deputy-chairman of that firm. The consideration for the sale was £1.6m, satisfied by the issue of 13 million new ordinary 10p shares in Stanley Gibbons at 12.25p each. He was a past president of the International Federation of Stamp Dealers Associations and was the founder of
Postal History International magazine in 1972. In 2008, he was invited to sign the Roll of Distinguished Philatelists. ==Death and legacy==