Mr Cameron said Mr Brown was not telling 'straight truths' to the public
Shadow cabinet members will have to give up any second jobs by December, party leader David Cameron has said.
He said while he did not want to see the Commons full of "professional politicians" it was necessary to focus "100%" on the general election.
He also said there was a "thread of dishonesty" running through Gordon Brown's premiership.
The Tories and Labour had been arguing about each others' cuts and spending plans for weeks.
Senior Tories are among MPs to find their lucrative second jobs under the spotlight, two days before a new rule insisting MPs declare all outside earnings comes into force.
MPs have had to name outside employers and directorships in the Register of Members' Interests but had not had to reveal how much time they spend on second jobs and only had to indicate salaries if it related to their work as an MP.
Speaking at a news conference the Tory leader said having outside interests was not incompatible with being an MP.
Mr Cameron said: "My shadow cabinet have, however, recognised that we are in a particular period at the end of a five-year Parliament where it does become necessary to demonstrate 100% focus on Parliament, politics and setting out our credentials as an alternative government.
"So they've decided that from the end of December they won't have any outside interests."
He said he believed it was the "right step to take" to make his frontline team focus on the upcoming general election.
He said it meant all of his shadow cabinet members in the Commons, and shadow leader of the Lords Lord Strathclyde would take part - although unsalaried Tory peers would not.
The Conservatives have also released details of the shadow cabinet's outside earnings two days early.
Among high earners are Michael Gove, the shadow schools secretary, who gets £5,000 a month for his columns in the Times, shadow business secretary Ken Clarke who receives £38,000 a year as a non-executive directory of Independent News & Media and David Willetts who is paid £60,000 a year as a pensions adviser.
Several senior Tories, including William Hague who last year earned about £230,000, from books, speeches and advice to private companies, had already indicated they were to abandon outside roles.
Other MPs who have found their second jobs under the spotlight are Labour's Nick Raynsford, who reportedly received £148,000 from six private sector jobs last year and the Lib Dem MP John Hemming, who gets more than £200,000 a year from his software company.
Earlier Business Secretary Lord Mandelson told the BBC there would be no comprehensive spending review - when the government sets out its spending plans - until after the next general election.
He said the government was "not in a position, in June 2009, to be able to forecast what growth will be and what the performance of the economy will be in 2011".
But Mr Cameron said it was "nothing to do with" economic uncertainty: "It's a blatant attempt to cover up the truth about Labour's cuts."
He accused Mr Brown of having "lost all connection with telling straight truths to the public".
He said: "I believe there is a thread of dishonesty running through this premiership."
He said there had been a "pattern of deception about public spending" and said he preferred to fight the next election on "a straightforward, frank and honest platform".
"That would be the worst of all, you go into an election pretending you are not going to have to make spending reductions, then you have to make them and then you really do have riots on the street because people lose all faith in their politicians."
He added: "I accept that we have more to do, more to say". However he said they were "way past" Labour who had not accepted reductions had to be made.
A spokeswoman for the Treasury has said no decision has been taken on whether there would be a Comprehensive Spending Review this year. Schools secretary Ed Balls told the BBC on Sunday it was a matter for the chancellor.