Millicent Holdings has paid £2.4m for the two companies that formed part of Stanley Gibbons' interiors division.
However the deal does not include the Mallett inventory, the rental income from the former Mallett New York premises, the Bloomsbury auction and retail business and its interests in fair Masterpiece London.
Stanley Gibbons will use the proceeds to pay down debt. It said Dreweatts, Mallett and the Bloomsbury businesses made an operating loss before exceptional costs of £4.1m in the year to March 2016 and £2.1m in the six months to September 2016.
Stanley Gibbons will retain ownership of coin group Baldwin's and Baldwin's of St James's joint venture.