BlackRock's "fast-exit" rule, which went live in December and has not previously been reported, will see such companies removed in 45 days at most rather than 90 days previously. The ruling covers 35 of its European listed ESG ETFs that track MSCI indices.

The change, which affects 'custom' funds containing $55.5 billion in assets, follows conversations with German wealth managers, who were keen to see poor ESG performance reflected more quickly across the ETFs, a BlackRock spokesperson said.

"We found that there was a desire to re-examine the timescales around the removal of companies with the worst controversies," the spokesperson added.

(Reporting by Virginia Furness; Editing by Kirsten Donovan)

By Virginia Furness