Sir Martin Sorrell could gain �44m over five years

The plan could be worth �122m over five years, with up to �44m going to chief executive Sir Martin Sorrell alone.

The payout is linked to WPP's business performance, but a previous vote was postponed amid criticism that the set targets were not tough enough.

Sir Martin has defended the deal as not a bonus but an "investment scheme."

'Extraordinary scheme'

Executives are expected to use their own money to buy about $30m (�16.7m) worth of WPP shares, Sir Martin told BBC Radio Five Live's Weekend Business programme.

Payouts would only materialise if the advertising firm stayed among the top two companies against a sample of 14 rivals during a period of five to nine years, he argued.

"It's not a bonus or options scheme," Sir Martin said.

"This is not a 'heads I win, tails you lose' scheme."

But critics like Sarah Wilson, managing director of Manifest, have complained that performance targets set for the "potentially... extraordinary scheme" were "far too vague".

Speaking to the BBC's Today programme, Ms Wilson - whose company advises large shareholders on voting issues - said it was the size of the pay-out that was concerning shareholders.

The plan envisages that managers' WPP shares will be matched five-to-one if targets are met.

"The company could not do very well in total shareholder return, and the rewards for managers could still crystallise," Ms Wilson warned.

Too much power?

The bonus plan was put to the vote on Friday at the company's EGM - which was postponed from 7 April to 16 April because of criticism of the bonus scheme.

Shareholders approved the plan on by a vote of 79.8% in favour to 15.15% against, with 5.05% abstaining.

The influential National Association of Pension Funds was in favour of the incentive scheme.

But others disagreed. Alan McDougal, managing director of PIRC, which advises institutional shareholders, said the WPP bonus scheme went too far for too little performance.

"It gives executives too much power over their own pay," he said.

WPP has also been criticised, like other large companies, for not dealing with institutional shareholders properly.