Deutsche Bank and Citigroup have admitted anti-competitive activity by exchanging sensitive information on UK government bonds between 2009 and 2013, Britain's anti-trust watchdog said Wednesday, as it provisionally found five banks in breach of competition rules.

HSBC, Morgan Stanley and Royal Bank of Canada, meanwhile, have not admitted any wrongdoing over the alleged sharing of information in one or more one-to-one conversations between a small number of traders in Bloomberg chatrooms in the aftermath of the global financial crisis.

Britain's Competition and Markets Authority (CMA) said in a statement it would consider further representations from the banks before reaching a final decision on its next steps and the possible issue of financial penalties.

"These alleged activities are ... very serious and warrant the detailed investigation we have undertaken. This could have denied taxpayers, pension savers and financial institutions the benefits of full competition for these products, including the minimisation of borrowing costs," said Michael Grenfell, Executive Director of Enforcement at the CMA.

The CMA said the conversations are alleged to have related to the buying and selling of UK government bonds — specifically, gilts and gilt asset swaps — and included details on pricing and other aspects of trading strategies.

The antitrust regulator has yet to decide if there was sufficient evidence of an infringement of competition law for it to take enforcement action against any of the banks. Until then, no assumption should be made that any of them had broken the law, it said.

Having alerted the CMA to its involvement, Deutsche Bank will not be fined if the provisional findings are upheld. Citi also struck a settlement with the CMA and will also likely receive a discount if a fine is imposed.

A Deutsche Bank spokesperson said the bank had secured "provisional immunity" after proactively reporting the activities, which took place before 2014. Citi said it had cooperated fully with the CMA on the matter and was "pleased to put it behind us."

A spokesperson for Morgan Stanley said it disagreed with the CMA's provisional findings and intended to contest them.

"Morgan Stanley cooperated fully with the watchdog during the investigation and will continue to engage in the process," the spokesperson said.

HSBC denies the allegations, and will continue to make its case while awaiting the CMA's final decision, the London-based bank told Reuters in an emailed statement.

RBC told Reuters said it was unable to comment on an ongoing regulatory matter, but had cooperated fully with the CMA and took any allegation of employee misconduct very seriously.

In the wake of the financial crisis, the Bank of England shored up the UK economy and markets by buying UK government debt, also known as gilts, via regular buy-back auctions.

Those auctions prompted some of the alleged exchanges of information among some of the banks involved, the CMA said.

Financial sector workers use Bloomberg chatrooms to communicate with customers and colleagues. The company, which is a Thomson Reuters competitor, is not being investigated.

Bloomberg did not immediately respond to a request for comment.