The stake has been acquired by Risk Capital Partners, an investment vehicle of which Johnson is a member. It now plans to expand Patisserie Valerie, which presently has 10 branches in London, on a nationwide basis.
Johnson, who now adds the title of chairman of Patisserie Valerie to his CV, said: "We have significant experience of rolling out successful food and drink concepts, including Pizza Express, Strada and Giraffe.
"Patisserie Valerie is a much-loved institution with tremendous heritage. We are confident there are many upscale locations across Britain's cities that would love the authentic pastries, cakes and savouries supplied by Patisserie Valerie."
Johnson was the surprise appointee to the role of chairman at Channel 4 in January 2004. Earlier this year, he was reappointed and will remain in the role until 2010, during which time he will oversee its attempts to move into digital radio and negotiations with the government for financial help during the digital switchover.
Johnson started his career in advertising with full-service agency BMP, subsequently joining Kleinwort Benson as a media analyst. He became famous when he floated the Pizza Express chain in 1993.
Patisserie Valerie is a London institution, and was opened in 1926 on Frith Street by a Belgian woman called Madam Valerie. When that branch was bombed during World War II, the shop moved to its present location on Old Compton Street.
Over the last 15 years, the shop has opened new branches around London, including the upmarket shopping areas of Knightsbridge, Kensington and Marylebone Village, and one in the City.
Risk Capital Partners acquired a stake in Seafood Holdings, which supplies fish to many upmarket restaurants. It also owns the family-friendly restaurant chain Giraffe, design group Loewy, and the Greyhound Racing Association.
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