(Adds link to FACTBOX)
* Average (mean) gender pay gap 30.3 pct at 42 firms
* Mean gender bonus gap 66.5 pct, data shows
* National median gender hourly pay gap 9.1 pct in 2017
* FACTBOX - Investors with widest gender pay gap
LONDON, April 4 (Reuters) - Fund managers in Britain, who hold other firms to account over their corporate governance, have among the highest gender pay and bonus gaps themselves, new data showed.
The average gap between pay for men and women at the 42 investment companies which had released the figures to meet the British government's demand was 30.3 percent, while the mean gender bonus gap was 66.5 percent, government and company data released over recent weeks shows. https://tmsnrt.rs/2Ej86M9
That compares with a national median gender hourly pay gap for full-time employees of 9.1 percent in 2017, according to Britain's Office for National Statistics.
One of Britain's most high-profile female chief executives, M&G's Anne Richards, told a recent conference that fund management was "one of the worst industries, there's no doubt about it", with the gap worsening over the years.
Most companies which released a report explaining their particular data on pay, said the gender gap was the result of fewer women holding more senior roles, while several said they had plans in place to close the gap.
Rachel Lord, head of Europe, Middle East and Africa for the world's biggest asset manager, BlackRock, called the government's gender pay gap drive "one of the most important things I've seen around equality in the last 30 years".
"I don't think any of us like where the numbers are... it's a blunt instrument; the calculation is kind of odd, but it doesn't matter, it shines a light on how we have to do more."
Corporate governance teams at major fund firms are increasing their engagement with the boards of large companies they invest in about the way they treat staff - on behalf of their investors who include retail savers and pension schemes.
A recent example is the debate about zero-hours contracts at firms such as Sports Direct, which drew the ire of the government and fuelled a wide-ranging review of corporate governance last year.
This has already led to some changes to the country's corporate governance code, making it important for asset managers to be seen to be performing well on the same measures.
"There will be additional scrutiny, so it will be necessary for asset managers... to have a look at what they're doing and lead by example," said Joe Dabrowski, Head of Governance and Investment at the Pensions and Lifetime Savings Association.
(Additional reporting by Huw Jones, editing by Sinead Cruise and Alexander Smith)