The new estimates are for those five UK agencies (see table, below) that cannot enter the Top 150, owing to the Sarbanes Oxley Act, but also do not submit any individual Companies House data.

In the annual league table, published last week, PRWeek made estimates for this difficult category of agency, based on a staff headcount figure multiplied by average productivity per head - £78,362 revenue for each staff member - among those agencies able to enter the leagues.

However, it has been pointed out that this average may have been too low, bearing in mind the size and nature of these five agencies. PRWeek has therefore re-estimated, based on average productivity of the top 10 agencies that entered, which gives us a figure of £106,549. The new results, also with slightly revised staff numbers, can be seen in the new table.

PRWeek's formula was dev­eloped last year by a panel of experts including PRCA director general Patrick Barrow and Willott Kingston Smith partner Esther Carder.

Barrow, who continues to support the approach but did not audit the recent figures, said: ‘It is important that the industry possesses this gauge of relative standing and the formula devised last year ­allows this. Of course, it's imperative that the figures are robust and the PRCA is glad to see a revision that reflects what we know to be the health of the sector.'

Restated top 150 figures (NEW estimates)

Sarbanes Oxley affected agencies without Companies House entry