Aviva said the allegations so far were serious enough for it to end its membership of the lobby group immediately, even as an independent inquiry commissioned by the CBI and a police investigation are ongoing.

"In light of the very serious allegations made, and the CBI's handling of the process and response, we believe the CBI is no longer able to fulfil its core function - to be a representative voice of business in the UK," an Aviva spokesperson said.

The CBI, which says it represents 190,000 businesses, has hired a law firm to conduct an investigation, which is expected to be published on Friday.

The British Insurance Brokers' Association cut ties with the CBI, the Financial Times reported on Monday.

Last week, the City of London Police opened an investigation into what the CBI called "a serious criminal offence" after the Guardian newspaper said a female member of staff had claimed she was raped by a manager at an office party.

Since then the Guardian has reported claims by a second woman that she was also the victim of rape by CBI colleagues.

The CBI last week sacked its director general Tony Danker for what it said was conduct which fell short of what was expected from someone in his position. His departure was not linked to the criminal allegations, the Guardian reported.

In a statement published on Friday, the CBI said an urgent root-and-branch review of its culture was proceeding.

"While the CBI was not previously aware of the most serious allegations, it is vital that they are thoroughly investigated now and we are liaising closely with the police," CBI President Brian McBride said.

"The board will communicate its response to this (the independent investigation) and the other steps we are taking to bring about the wider change that is needed early next week."

(Reporting by Simon Jessop; Writing by Sarah Young; Editing by Jason Neely, William Schomberg and Kim Coghill)

By Simon Jessop and Sarah Young