And he added that there were even more significant "fundamental" problems in their attitude to lending to businesses with productive ideas.
Adam Posen is a US economist who sits on the Bank's Monetary Policy Committee, which votes every month on whether to change the level of interest rates.
He said on BBC Radio 5Live that UK banks were not doing enough to support the real economy.
"How much of that is because they are reluctant, risk averse jerks and how much because there is something more fundamental at work - I think it's as much fundamental if not more so," he explained.
He said that cutbacks in lending to small, medium and new businesses had been "tremendous".
And Mr Posen commented that banks were "choosing to lend to roll over debts to large borrowers...but they're not issuing new loans to new borrowers."