The figure emerged from accounts filed at Companies House by the four-time PRWeek Consultancy of the Year, which has never taken part in PRWeek’s Top 150 PR Consultancies report.
The accounts, for Blue Rubicon Limited, include its consumer PR operation Surname & Surname and its consultancy arm Thirty Six Strategy, but not its recently launched Dubai and Qatar offices.
During 2013 it added more than £3m to its top line to achieve a turnover of £21.1m. This puts it in the same league as Good Relations Group, Exposure and Four Communications, which are ranked in PRWeek's top 25 agencies.
Gordon Tempest-Hay, CEO of Blue Rubicon, said: "None of our income was acquired. We grew at this rate thanks to a combination of securing more work from existing clients, a very high new business conversion rate and an ever-increasing flow of work from outside the UK."
The accounts cover the calendar year 2013, which came before the acquisition of public affairs agency Open Road in February.
It was the first set of results since agency founder Fraser Hardie opted to sell a stake to private equity company Lloyds Development Capital (LDC), which valued the agency at around £30m, in December 2012.
The fact that the agency slightly increased its profit margin to 23.6 per cent (operating profit of £3.876m with gross profit of £16.408m) indicated it was a year of stable growth.
Account wins including Guardian Soulmates and Cancer Research UK added to a client line-up already featuring Sainsbury’s and O2.
With an average of 146 staff during the year (up from 127 the previous year) its gross profit per head was £112,384.
The highest-paid director (who was not named in the accounts and whose identity was not revealed by the agency) received a salary of £177,000, down from £201,000 in 2012.
Blue Rubicon Limited paid out a dividend of £2.5m, which Tempest-Hay said was to provide working capital to overseas offices, repay loan interest and cover the costs of its holding company.