AS revelations over MPs’ expenses draws to a close, attention has turned to those MPs who earn another income from a second job.

Tory leader David Cameron has said his shadow cabinet ministers will have to give up their second jobs by December to prepare to fight a general election.

He said he didn’t want the Commons full of “professional politicians”, but others argue that experience can benefit the House and decision making.

It is the latest debate after the expenses scandal.

But Douglas Carswell, the MP who effectively ousted the last Speaker by tabling a motion for Michael Martin’s removal, has warned against banning second jobs.

He said: “Anyone on the ministerial pay roll effectively already has a second job.

“Banning second jobs would prevent anyone with other careers from playing an active part in how the country is run.”

The Tory MP for Harwich and Clacton said it was difficult for anyone other than professional politicians to become an MP, and that he would like to see more part-time MPs who have other careers.

The Tory backbencher added: “Banning outside interests means MPs will have only inside Westminster interests.

“It will mean the executive and party whips have a total monopoly to determine an MP’s career.

“That means less scope for the independent-minded and more power for the executive over those we elect to represent us.”

Mr Carswell said the move would mean Parliament would be full of MPs who aspire to be in Government, with no one to hold it to account.

From today, MPs will have to sign up to a new register, which is expected to reveal the revolving door between Government and business which has seen some politicians walk into highly paid positions.

Among the Conservative 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.

Labour’s Nick Raynsford MP also reportedly received £148,000 from six private sector jobs last year, while Lib Dem MP John Hemming receives more than £200,000 a year from his software company.

Colchester MP Bob Russell said he believed MPs with another job could not be performing their political duties to the best of their ability.

He said: “Frankly, I don’t see how anybody doing this job properly has the time to have a second job.

“I think it can sometimes be acceptable, for example, in the case of Robert Goodwill, the Scarborough MP, who has a farm in Yorkshire. He employs a farm manager, but pitches in himself at weekends.

“That is one thing, but if people are doing other work during the week, it is going to prevent them giving enough time to their role as an MP.”