Regulators are scrutinising relationships that banks such as HSBC, Deutsche Bank, Société Générale and Crédit Agricole may have had with a former Barclays trader

The rate-rigging scandal that has enveloped Barclays appears to be widening as questions are raised over the relationship between its staff and employees at other banks in the ongoing investigations into attempted interest rate manipulation.

According to the Financial Times, regulators are scrutinising relationships that banks such as HSBC, Germany's Deutsche Bank and the French banks Société Générale and Crédit Agricole may have had with a former Barclays trader, raising questions over the allegations relating to attempts to manipulate the European equivalent of Libor, known as Euribor.

According to the FT, sources suggest that one of the unidentified traders in the regulatory notices issued last month may be Philippe Moryoussef.

Barclays was hit with a £290m fine last month for attempting to manipulate interest rates. Moryoussef is not accused of wrongdoing. The FT said he had not been interviewed by any authority investigating potential manipulation of Libor or other benchmark rates.

Moryoussef worked at Barclays between 2005 and 2007 before joining other banks including Royal Bank of Scotland, according to the FSA register. He left the Japanese bank Nomura last month. The bank said: "Nomura is aware of the investigation into the setting of Euribor and Libor rates. We would point out that Nomura is not a member of either the Euribor panel or the Libor panel, and therefore has no role in the setting of those rates."

According to the FT, the regulators are said to be looking at suspected communications between Moryoussef and Michael Zrihen at Crédit Agricole, Didier Sander at HSBC and Christian Bittar at Deutsche Bank, none of whom are thought to be still employed by these banks. No allegations of wrongdoing have been made against any of these individuals by regulators or their former employers. None of them could be reached for comment.

The Barclays fine covered two broad timeframes: the period between 2005 and 2007 when Barclays was said to have attempted to manipulate rates for traders; and the period of the financial crisis when it reduced its submission to the rate-setting panel for fear of attracting negative publicity. The latest revelations cover the period before the 2008 financial crisis and focus on Euribor. At least 20 banks and financial firms are thought to be helping the authorities in many countries with their inquiries into both Libor and Euribor.

Barclays – whose chief executive Bob Diamond has quit – has argued that it was the first to settle. In an internal memo sent last week, co-signed by the chairman, Marcus Agius, Barclays apologised for the impact of the scandal on staff, but added: "As other banks settle with authorities, and their details become public, and various governments' inquiries shed more light, our situation will eventually be put in perspective."

On Wednesday night Deutsche Bank referred to its latest regulatory disclosure in which it stated that it had "received various subpoenas and requests for information from certain regulators and governmental entities" around the world and that these related to "various periods between 2005 and 2011".

HSBC declined to comment beyondreferred to a statement in its annual report in which it stated that "various regulators and competition and enforcement authorities around the world" are "conducting investigations related to certain past submissions made by panel banks" in connection to Libor.

Société Générale said it was "fully co-operating with regulators over the Euribor investigation which also includes many other banksand so far no allegations of wrongdoing by any authorities have been made against us".

Crédit Agricole said in a statement that it had responded to requests for information from authorities but "has not been accused of any wrongdoing." It added that it only became a contributor to the Libor panel in 2010.