MPs will be forced to declare all income and time related to their second jobs from today under new rules introduced by the government in an attempt to increase transparency.

Previously MPs had to name their outside employers and directorships in the Register of Members' Interests but were only required to disclose income related to their work in parliament.

The new rules on outside interests were agreed in April before the expenses scandal began.

Harriet Harman, the Leader of the Commons, said: “I believe that the public are entitled to know the source of work for payments to an individual MP, how much is being paid, and what the MP is undertaking for that payment.”

She added: “The public want to know who, other than they as taxpayers, is paying an MP.”

Labour MP John Mann welcomed the new guidelines as an “important step forward” but called for a ban on second jobs and on MPs profiting from their inside knowledge.

“It's a form of insider dealing and it's entirely undemocratic and it needs banning,” he said.

But Conservative backbencher Douglas Carswell warned that banning second jobs would reduce MPs’independence from their party machines.

He said: “Abolishing outside interests would make all MPs totally beholden to the party whips.”

He added that if MPs became “financially dependent upon their party machines" they would be less able to hold the government to account.

David Cameron has promised that all members of his shadow cabinet will give up their second jobs by the end of the year.

The Conservative leader warned that Parliament would be diminished if it was only filled with "professional politicians" but said it was right for shadow ministers to focus on politics in the run-up to a general election.

In total the shadow cabinet earn around £479,000 a year from second jobs. High-earners in the party include William Hague, the shadow foreign secretary, who earns £50,000 a year from JCB, the construction company and £25,000 from AES Engineering. He has already given up his lucrative after-dinner speeches.

Oliver Letwin, the party's policy chief, is paid £60,000 a year by NM Rothschild for working eight hours a week. While Michael Gove, the shadow children's secretary, earns £60,000 a year for his Times column.

Many of Cameron's team rushed to give up their second jobs before earnings were published over fears that the public would be outraged following the expenses scandal.