Barclays is in turmoil following an interest rate-rigging scandal that led to the departures of Diamond and Chief Operating Officer Jerry del Missier on Tuesday and is under pressure from politicians and regulators to change its culture, possibly slimming down its investment banking operations.

"Although this could have potentially positive implications over the longer term, the uncertainty surrounding such a change in direction is credit-negative in the short term," said Moody's, which lowered its outlook for the standalone bank's financial strength to negative from stable.

Barclays was last month fined nearly half a billion dollars for its part in manipulating a key interest rate which underpins financial transactions worth an estimated $360 trillion.

Reuters reported on Thursday that Britain's financial regulator warned the entire Barclays' board in February that the bank's culture needed to change.

S&P on Thursday lowered its outlook for Barclay's long-term rating to negative from stable citing management upheaval and the strategic uncertainty currently facing the bank.

"We see potential for the eventual new CEO to review the current scope of Barclays activities, particularly if that person were an external hire," it said.

Fitch said the impact of the Libor investigation didn't alter its view on Barclays and said it was premature to speculate about any change in strategic direction.

Barclays announced Diamond's resignation on Tuesday and his departure was followed hours later by that of del Missier.

Marcus Agius was moved to the role of executive chairman to oversee the hunt for Diamond's successor, just 24 hours after announcing his own intention to step down.

"I think the bank is clearly in a state of flux at the moment," Dominic Rossi, Global CIO Equities at top-ten investor, Fidelity Worldwide Investment, said at a briefing earlier this week.

Another UK-based shareholder told Reuters he had held off holding conversations with Barclays until the situation had calmed down.

"We'll try and have a measured conversation with them all early next week. Hopefully emotion will die down a bit and then when we've got some clear heads," he said.

Moody's said Barclays could struggle to find a suitable candidate to step into Diamond's shoes.

"The bank could be challenged to replace the three senior staff and in particular find a new CEO who not only has a sufficient understanding of the investment banking business to run Barclays, but also has the credibility and ability to swiftly address the weaknesses that the Libor incident revealed and stakeholders' perceptions of the investment bank," it said.

Oriel Securities analyst Mike Trippitt said more senior staff could depart Barclays as the bank struggles to get to grips with the fallout from the rate rigging scandal.

"Given the leadership gap and uncertainty over the future of the business, the risk of further staff departures should not be underestimated," he said.

Trippitt said political pressure was likely to influence the future shape of Barclays but warned interference could reduce the value of any asset sales.

"The government should be mindful that forced deleveraging (like RBS) will reduce the potential capital emerging from BarCap's wind down," he said.

Libor is a market benchmark published by the British Bankers Association (BBA) based on a survey of what London banks tell its compilers they have to pay to borrow from their peers, in various currencies and for different periods. It is used to price financial contracts around the world, ranging from complex interbank transactions to consumer mortgages and student loans.

The Libor figures submitted by banks are compiled by Thomson Reuters, parent company of Reuters, on behalf of the BBA.

(Additional reporting by Wayne Cole; Editing by Elaine Hardcastle)

• A Permanent Economic Emergency