London Mayor Johnson was answering a question on the issue of dodgy city workers being jailed for criminal banking acts.
"I think you should jail anybody who is guilty of criminal behaviour.
"For all the grievous mistakes and semi-criminal acts that the bankers got up to in the period up to the crash, absolutely nobody has been successfully prosecuted. Nobody has been sent to prison and there's a huge amount of anger about that.
But he added: "I don't see any long term advantage in continuing with an orgy of banker bashing."
Comedian Russell Brand chipped in: "I think an orgy of any kind would be great, but one which focuses on banker bashing would be the greatest orgy I can imagine."
On the question of bankers being jailed Brand said: "Look for people who've got loads of bonuses and loads of money. They are the people that are criminal. They are the people that need to be prosecuted.
"We need to see punitive measures immediately deployed so it doesn't continue to occur.
"People need to go down and it's the people that have got the money that need to go down."
But the debate turned on a point Johnson made when talking about jailing politicians involved in the banking crisis.
"You could probably frame a law for bankers, but what about the Labour government who were in power in the period leading up to the crisis?
"There they were sitting there deregulating. Gordon Brown went to the City of London in June 2007 and said we are entering a golden age of banking in the City of London. What kind of signal did that send? Now, should Gordon Brown be send to prison?" he asked to shouts of "yes" from the studio audience.
"Tessa Jowell (also on the panel) was part of that government - should she be sent to prison? I sincerly hope not. I would come and visit her in prison."