Seven Publishing, which publishes the food title Delicious, was set up with 20 shareholders. Seamus Geoghegan, the managing director, Jo Sandilands, the editorial director, and Michael Potter, the chairman, hold three of the largest stakes.
GMG was approached for further funding and has now become the single largest shareholder with a 27 per cent stake. It has contributed £2 million to support Seven's growth in the consumer magazine market.
Seven has also attracted £500,000 in funding from other interested parties.
The increased investment will be used to promote Delicious and to back the launch of a second title, which will be announced soon.
Potter said: "We would have liked to have promoted Delicious more than we have and now we can make up for this. We will also be looking at launches and possible acquisitions during the year. There will be other spin-offs - books and exhibitions - from the company in due course."
Seven was set up by Potter, who founded Redwood Publishing, Geoghegan, a former director of BBC Worldwide, and the former Capital radio programme director Sandilands. It won the rights to publish the Australian monthly Delicious in the UK, after bidding against BBC Magazines.