WPP shareholders will take part in a non-binding vote on the company's 2015 remuneration report on June 8.

ShareSoc, which advises individual private investors in British companies, said it acknowledged the positive performance at the advertising company in recent years but said the quantum of Sorrell's pay and incentives was unnecessarily high.

ShareSoc estimates that Sorrell, who earned 70 million pounds in 2015, has been paid 191 million pounds since 2009 and his 1.8 million potential future share awards would be worth an additional 78 million pounds if they all vested.

The entrepreneur, who has drawn sharp criticism among investor groups over pay for several years, has an annual bonus maximum opportunity of 435 percent of salary and a long-term incentive annual award of 974 percent of salary.

He also received 1.5 million pounds of dividend equivalent payments and 460,000 pounds of pension contributions, "even though he is 71 years old and well past the normal retirement age", ShareSoc said.

"In view of his shareholdings and existing incentive awards, I don't see why he needs to be given any more incentives. I don't think it will make him work any harder," ShareSoc director and remuneration spokesman Cliff Weight said in a statement.

"It is yet another example of remuneration creep," he said.

WPP Chairman Roberto Quarta defended WPP's pay plan in the company's annual report last month, pointing out the scale of Sorrell's contribution to the company's "outstanding set of returns to shareholders".

(Reporting by Sinead Cruise; editing by Jason Neely)