The amount of the deal was not disclosed.
Broadgate Mainland represents national and international brands including BNY Mellon, Baillie Gifford, Durham University Business School, St James’s Place Wealth Management and Woodford Investment Management.
As part of Four, Broadgate Mainland will be rebranded as Four Broadgate and will focus on the delivery of communications programs within the specialist areas of financial services, professional services and education.
The acquisition followed a £10m investment of equity finance from BGF and a debt facility from HSBC earlier in August 2015.
Four provides services including public relations, public affairs, marketing, sponsorship, digital & content and media planning & buying with a particular focus on the property, travel, culture, healthcare, financial services and public sectors.
The company employs over 220 staff and has over 600 clients including Etihad Airways, The Man Booker Prizes, Sotheby’s International Realty, InterContinental Hotels Group and American Express.
The firm also has offices in Edinburgh, Abu Dhabi and Dubai.