Barclays faces renewed scrutiny of its emergency fundraising during the financial crisis after the City regulator reopened its investigation into the bank’s cash call with Qatar.

It is understood that the Financial Conduct Authority (FCA) interviewed individuals for its case in recent weeks, in a move that ratchets up the pressure on the lender and could result in the regulator increasing a £50m fine it previously slapped on the bank.

Barclays is already subject to a criminal investigation by the Serious Fraud Office (SFO) into the 2008 fundraising, a probe that is approaching a critical juncture. The fraud investigator has said that it plans to make a decision on charges by the end of this month.

Barclays is still overshadowed by the actions it took during the credit crunch, when the desperate bank avoided a Government bailout by making two cash calls with Middle Eastern investors from Qatar and Abu Dhabi, raising £4.5bn in June 2008 and a further £7.3bn in October. At the time, the lender was led by chief executive John Varley and chairman Marcus Agius.

The way the bank secured the investments has become shrouded in controversy, however. As well as the FCA and SFO probes, financier Amanda Staveley has launched a legal battle to recoup more than £700m from Barclays in fees she claims her firm PCP Capital Partners is owed for helping to arrange the cash calls.