The chairman of Barclays is expected to fall on his sword with his bank engulfed by the Libor rate-rigging scandal.

Marcus Agius will announce his resignation at 7am on Monday after informing fellow board members of his decision on Sunday, according to reports.

He will acknowledge that standards of behaviour at Barclays had been unacceptable and that the affair had dealt a devastating blow to the bank's reputation, the BBC said.

His resignation comes after signs of shareholder moves to replace him in the role. He is due to face MPs on the Treasury Select Committee on Thursday - a hearing that is expected to go ahead irrespective of his decision to quit.

Pressure remains on Barclays chief executive Bob Diamond, who will also face a grilling from the committee on Wednesday. There were growing questions about how much he knew about what was going on after it emerged that Barclays staff mistakenly thought they had been instructed by the Bank of England to lie in their Libor submissions.

The Financial Services Authority's report into the bank said there had been a misunderstanding arising from a conversation between BoE deputy governor Paul Tucker and an unidentified senior Barclays manager on October 29, 2008.

Business Secretary Vince Cable has backed calls for a criminal investigation into bankers involved in the affair. The Liberal Democrat Cabinet minister said the public could not understand why the perpetrators of "what looks like a conspiracy" were allowed to "just walk away".

The potential for prosecutions arising from the scandal has been downplayed by Treasury sources who point out that there are no criminal sanctions in place for manipulating the inter-bank lending rate, or Libor.

Libor is set on a daily basis by panels of banks and used to help set "swap rates" - the borrowing rate between financial institutions. These rates in turn are used to price a vast range of products such as corporate loans and fixed-deal mortgages.

Lord Blair, a former head of Scotland Yard, added his weight to the call for a criminal investigation. He said there had to be police inquiries into revelations that traders at Barclays, Royal Bank of Scotland and other banks had tried to fix the rate.