London mayor expresses sympathy with those who want former PM locked up and says Chilcot report should be published now

People who believe Tony Blair should be imprisoned over the Iraq war have their hearts in the right place, Boris Johnson has said as he called for the immediate publication of the Chilcot report into the war.

Speaking on his LBC phone-in, he spoke of the "catastrophic consequences" of the Iraq invasion but described the former prime minister as an "eel-like customer" who would use his legal skills to avoid prosecution.

Johnson made clear he sympathised with a caller who thought Blair should be imprisoned. The London mayor said: "He is a very, very adept and agile lawyer. Our caller who thought he was going to be imprisoned for what he did in Iraq – his heart is in the right place. It's just not going to happen."

He declined to rule out standing for parliament at next year's general election, raising the prospect that he would hold two jobs as London mayor and MP from 2015 to 2016. Asked by LBC presenter Nick Ferrari to say no to "Boris two jobs Johnson", he said: "I am very proud of what we have achieved in London but there is a lot more to do."

Asked whether he would ever be prime minister,he said: "Of course not," adding: "The chance[s] of me being prime minister are about as big as the chances of me being locked in a disused fridge interred in a … what is it?"

He made clear he had doubts about the proposed Pfizer takeover of AstraZeneca saying he would be asking searching questions of the US pharmaceutical company if he were in office.

"Politicians can't be entirely aloof from this and it would be very important to establish that Pfizer is genuinely committed to R&D in this country and that it won't in any way damage what is the incredible success, particularly of London and the south-east, in dominating the European scene in life sciences and biotechnology. It would be a great shame if that were to be lost."

On the Iraq war, he admitted he had voted in favour of military action in 2003 though he said he thought at the time that Blair's claims about weapons of mass destruction (WMD) were "nonsense". But he said he thought Blair would avoid prosecution.

Johnson, who was part of a campaign in parliament in 2004 to impeach Blair, told LBC: "It would be hard to mount criminal charges. You would have to show some sort of malfeasance in public office, which would be very difficult to prove.

"There will undoubtedly be people who continue to try to bring Tony Blair to justice in one way or another. I think it unlikely they will succeed … In the case of Tony Blair it will be quite difficult to secure a conviction. He is a very eel-like customer. It would be very unlikely you would get him."

He said the Chilcot inquiry into the Iraq war should be published without delay on the grounds that it was more than 10 years since the "whole disaster" had begun. "Somebody like me, who basically had good faith about what the British government was telling us, thought there must be a plan to deal with the aftermath in Iraq.

"I just could not believe it as things unfolded in the way that they did. I feel guilty because I voted for the wretched thing … I would like to understand more deeply on what basis a prime minister who, at that time, commanded so much trust, was able to persuade parliament and the country and me to go for war in Iraq with absolutely catastrophic consequences."

On WMD he said: "The more I listened to the debate back in 2003 I started to think it probably was a load of nonsense."

He said he supported the invasion because any successor to Saddam Hussein would be better than the "evil monster".

"I am afraid I listened to the government and thought that must be right – the Pentagon, HMG – they must have thought this thing through.

"They must have a plan. That was a total, total error. It was quite clear that the agenda was very, very feebly thought through and it was a disaster."