The Prime Minister said the proposal to offer small investors up to £4 billion-worth of shares below market value was only possible because the coalition's economic plan was working.
He insisted it would "help us recover billions more and pay down the national debt" and rejected Labour claims that the Lloyds offer had been made several times before.
Some weird looking bloke now singing 'Speed away in your getaway car..' at Cameron on #marr set.
I suspect he'll need to on May 8.— Piers Morgan (@piersmorgan) April 19, 2015
But shadow chancellor Ed Balls insisted Cameron had first made this promise ahead of the last election and in total announced it seven times.
Cameron looked most awkward when Marr asked him to confirm fox hunting was his "favourite sport". #Marr— George Eaton (@georgeeaton) April 19, 2015
He also criticised the Government's handling of the Royal Mail sale and warned against allowing the taxpayer to be "ripped off" a second time.
Cameron rejected Labour's claim and told BBC1's Andrew Marr Show it was the first time there had been a "retail offer to individuals so they can own shares in healthy, successful British banks".
Doesn’t David Cameron have a remarkably wrinkle free and smooth forehead for a man of his years? #marr— Mark Ferguson (@Markfergusonuk) April 19, 2015
He added: "The taxpayer put £20 billion into these banks and I want to get the money back. We have already recovered billions and this will help us to recover billions more to pay down the national debt.
"But at the same time I think having people in our country being able to own shares in healthy, successful British banks is the sort of country we should be building."
Never seen Cameron this tetchy & rattled. He knows he's in big trouble. #marr— Piers Morgan (@piersmorgan) April 19, 2015
Balls said he wanted to see Lloyds and RBS back in the private sector to get the nation's money back and the national debt down.
He told Sky News' Murnaghan: "Of course the public should be buying the shares but David Cameron promised this before the last election.
Cameron isn't usually stroppy on TV. Pressure? #Marr— Kevin Maguire (@Kevin_Maguire) April 19, 2015
"He has announced it seven times. It has taken him a lot longer than he thought.
"I want to make sure we maximise the long-term benefit for the taxpayer. I want to make sure we get the money in.
"If people buy the shares the money is coming to the Treasury."
Stroppy performance from Cameron here. He hasn’t had the crossover that Lynton promised and his campaign isn’t going as he planned #marr— Mark Ferguson (@Markfergusonuk) April 19, 2015
He said he would look at the idea of giving small savers a discount and consider it if he found it to be a fair deal for them.
The Labour frontbencher later called Cameron a "desperate Prime Minister with a faltering campaign".
Chancellor George Osborne set out plans to sell a further £9 billion tranche of the taxpayers' stake shares in the bailed-out bank in his final Budget of the last parliament last month.
Cameron: "Imagine the horror! This is the first time Scottish people might have a say in the government of the UK" #Marr— David Schneider (@davidschneider) April 19, 2015
Buyers who keep them for a year will be rewarded with a "loyalty bonus" of one additional free share for every 10 shares that they still hold.
After last week's announcement by the Tories to revive Margaret Thatcher's Right to Buy scheme, the move recalls another of her keynote policies to build a share-owning democracy.
Under the terms of the retail offer, buyers will receive a discount of at least 5% on the market price at the time of the sale, with priority being given to investors purchasing up to £1,000 worth of shares.
The minimum purchase will be £250 and there will be a maximum limit of £10,000.
Cameron denies that his private polling is pointing to him failing to get into No.10 #marr— Paul Waugh (@paulwaugh) April 19, 2015
The Government has already raised £9 billion from the sale of Lloyds shares, and the state's stake in the bank - which was 43% at the time of the bailout - is now down to 22%.
As with previous Lloyds share sales, the proceeds from the latest offering will be used to pay down the national debt.
Liberal Democrat Chief Secretary to the Treasury Danny Alexander told BBC Radio 5 Live the idea had been looked at several times but decided against "because it's not been clear that we'd be able, through this method, to get the money back for the taxpayer".
He added: "The British people have put a lot of money and made a lot of sacrifices as a consequence of the financial crisis, and as we are able to return these banks to the private sector, people should be able to benefit.
"The point I'm making about this Tory plan is, I'm not sure anyone can have any certainty it will actually happen... unless the Conservatives are saying that they'd sell these shares even if they didn't get the taxpayers' money back, and I think that would be a highly irresponsible thing to do."