Mr Hoon was a minister for more than 10 years
Labour MP Geoff Hoon has said he got it "wrong" and "should have known better" after he was filmed saying he wanted to profit from his government contacts.
Mr Hoon and two other ex-ministers were suspended for bringing the Labour Party into "disrepute" after revelations in the Dispatches programme.
The ex defence secretary said he was "guilty of showing off" and watching his remarks had been "excruciating".
Prime Minster Gordon Brown said his behaviour was "not acceptable".
Mr Hoon was one of a handful of MPs, including Stephen Byers and Patricia Hewitt, secretly filmed discussing employment opportunities with an undercover journalist posing as the representative of a lobbying firm.
Mr Byers told the company he was a "cab for hire" and that he had helped to influence government decisions on behalf of companies such as Tesco and National Express.
Current ministers rejected Mr Byers' claims as a "fantasy" and the MP later said that he had been boasting. The companies also denied Mr Byers had acted on their behalf.
The three Labour MPs have denied any wrongdoing and their cases are set to be investigated to the parliamentary authorities.
The Conservatives have called for a wider inquiry into questions of lobbying at the heart of government, a call rejected by Downing Street.
Mr Hoon, who is standing down at the general election, told the BBC that he had "certainly got it wrong".
"I should have known better," he said. "I should not have said some of the things I said.
"I accept that in the course of that conversation I said a number of things that because I thought I was engaged in what was an informal chat - wasn't leading to any particular position.
"I recognise that I was guilty of... showing off, I think is probably the best expression I could use. I was trying to impress, I was trying to demonstrate my knowledge and experience, background in a particular sector."
He added: "I watched parts of the programme on Monday night and it was excruciating. I don't stand up for some of the things I said, it was terrible."
But Mr Hoon insisted that he was offering "strategic advice" only, not seeking to lobby officials in return for cash, and that his discussions related to what he could do when he left Parliament.
"I made clear I did not and do not want to be a lobbyist," he said.
He said he was right to be looking for opportunities when he stepped down, likening himself to an employee "working his notice".
"I don't think it's entirely unreasonable to say that I should be thinking about the future. I also have responsibilities to my family. I have got to try to find a way forward."
Senior Labour figures rounded on Mr Hoon and the other former ministers after their interviews, Lord Mandelson describing Mr Byers' behaviour as "rather grubby'.
Prime Minister Gordon Brown said: "It's not acceptable behaviour. I think Geoff Hoon will recognise that, and hear the public view on this."
He said he wanted to "tighten up" the ministerial code of conduct and the rules MPs' business appointments and introduce a register of lobbyists, adding: "The cleaning up of this system has got to take place."
Mr Hoon, who lost his unpaid job as a UK adviser to Nato after the programme, said he had paid a "considerable price" for his mistake.
"Obviously I am very disappointed. I readily said to you that I got it wrong," he said. "I certainly would unreservedly apologise to anyone who feels I let them down."
While acknowledging the widespread anger within Labour at his actions, he said he was "disappointed" after 35 years in the party to have learnt about his suspension through the media.
Some colleagues had "expressed their sympathy about the way I was set up", he added.
Mr Hoon and Ms Hewitt led an aborted leadership coup against Gordon Brown in January, leading some commentators to speculate that their suspension was revenge for their actions.
Asked about that, Mr Hoon said: "Oh I hope nobody has been as petty as that. I think that would be quite wrong."