The Bank of England and Barclays were in almost daily contact over inter-bank lending at the end of October 2008, according to newly released emails.
The Serious Fraud Office (SFO) will launch a criminal investigation into the manipulation of the benchmark lending rate.
Former chief executive Bob Diamond is facing a battle to keep his £25m pay-off from Barclays after it emerged the bank's board is looking into its legal position on his entitlements.
Ratings agency Moody's has changed the outlook on Barclays' financial strength rating from stable to negative, saying the uncertainty over the bank's future direction is negative for bondholders.
The board at Barclays was told less than six months ago that the relationship between the bank's senior management and the City watchdog had "broken down", according to reports.
Bob Diamond has told MPs he feared Barclays would be nationalised during the credit crisis because of its high borrowing rate.
Barclays' submission of a memo to the Treasury Select Committee has revealed how Bank of England (BoE) officials advised the bank on LIBOR.
The FTSE 100 has risen in early trading as investors build on recent gains, but Barclays' share price remains volatile as investors react to CEO Bob Diamond's resignation.
The resignation of Barclays CEO Bob Diamond does not lessen the possibility of criminal proceedings against those involved, Chancellor George Osborne has warned.