BGF is believed to have taken a 20 per cent stake in Zone in return for the money. BGF senior investment manager Mark Nunny will also take a place on Zone's board.
Zone will use the cash to expand both in the UK and in Europe, and invest in data, video, mobile and CRM.
In addition to receiving external funding, Zone has hired Jim Kelly as a non-executive director to help with its growth strategy.
Since stepping down as chairman of Dentsu Europe and Mcgarrybowen in 2013, Kelly has worked as a consultant for digital, advertising and marketing agencies, and earlier last year took a non-executive director role at Karmarama.
James Freedman, Zone’s executive chairman, said: "In the past we’ve made acquisitions through cash-flow. With this new investment we’ll be able to further build our offering."
Zone was founded in 2000 and now has 185 staff in offices in London, Bristol, Berlin and Cologne. The agency is predicting that its turnover in 2015 will be £17 million.
The Business Growth Fund was established in 2010 and is backed by banks including Barclays, HSBC, Lloyds, RBS and Standard Chartered.