The Conservative party has joined forces with the main employers group, the CBI, in an attempt to dilute a new bribery bill that was meant to clean up corporate corruption in the wake of the BAE scandal.

More than 20 amendments have been put down by the Tories following pressure from the CBI against proposed legislation from the Ministry of Justice that had previously received cross-party support.

Campaign group Transparency International said it was "extremely concerned" that there was a deliberate attempt to derail future new laws that were vital to re-establish the international credibility of the British business community. It said: "The bill represents the best possible consensus that can be attained among a wide range of stakeholders on a modern, effective legal framework to prosecute bribery and make the UK compliant with the 1997 OECD anti-bribery convention."

London has faced increasing criticism that it has been good at pointing the finger at foreign countries that fail to tackle bribery while refusing to crack down sufficiently at home after a number of high-profile and embarrassing cases.

Britain has slipped to 17th place in the annual corruption perceptions index compiled by Transparency International and now trails Japan, Hong Kong and Austria.

Last week, four former executives from the London-listed mining group, Rio Tinto, were convicted of bribery in China while the UK's largest arms manufacturer, BAE, recently agreed to pay out almost £300m in US penalties as it finally admitted guilt over its worldwide conduct in the face of long-running corruption investigations.

Meanwhile, three UK directors of the engineering firm Alstom were arrested two weeks ago in dawn raids by fraud investigators and police over allegations that substantial bribes were paid to secure contracts abroad.

British bridge builder Mabey & Johnson was ordered to pay £6.6m in fines following corruption charges over payments alleged to have been made to win contracts in Ghana and Jamaica as well as a deal in Iraq under the "oil-for-food" programme.

The bribery bill was drawn up by the Law Commission and recommended the common law offence of bribery be replaced with a bill that specifically covers bribing foreign officials. A maximum of 10 years' imprisonment is allowed for all offences while corporate failure could involve an unlimited fine.

But the CBI is worried the bill in its unchanged form would leave British firms potentially barred from public contracts in the EU and would hamper their competitiveness.

Some of the Conservatives' proposed amendments to the legislation would involve prosecutors having to prove dishonest intent on the part of those handing out the bribes rather than just showing they were trying to gain an improper advantage.

The Conservatives were unavailable for comment but Jonathan Djanogly, shadow minister for corporate governance, has always insisted he favours the new legislation. In a blog on the Conservative party website, he has claimed: "This is an important bill in re-establishing our national credentials as champions of fair business dealings and trade transparency. I aim to ensure the bill is consistent, effective and covers existing gaps in the law."