The company won the contract after promising to cut costs and shorten campaign cycles for the 90 campaigns that Book Club Associates runs each year.
Book Club Associates is one of the biggest direct marketing spenders in the UK and its campaigns make use of more than 40m records.
Simon Swetenham, chief executive of Swetenhams, said: "The sheer volume of mailings and data used by BCA, combined with our buying power, flexible use of technology and expertise, means that we can work together to ensure maximum return on investment for each campaign at a time when companies need to reduce their data-buying costs without losing momentum in the marketplace."
Book Club Associates was formed in 1966 and is wholly owned by the German media giant Bertelsmann. It has turnover of more than £100m a year and has more than 2m members in its network of clubs.
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