Ed Miliband has called on David Cameron to ban MPs from having second jobs "to restore the reputation of this house" following recent allegations against two former foreign secretaries.
Mr Miliband accused the Prime Minister of not wanting to change the rules after the Government amended a Labour motion that MPs should only have one job.
The Labour leader recalled comments by Mr Cameron in 2009 when he said in opposition that "being a Member of Parliament must be a full-time commitment" and that "double-jobbing MPs" would not be allowed under his leadership.
Mr Cameron said Mr Miliband's proposal was "not thought through", adding: "I think the difficulty with your specific proposal is it would allow, for instance, someone to be a paid trade union official but it wouldn't allow someone to run a family business or a family shop."
Miliband hit back, saying: "Let's agree now we will rule out anyone being a paid trade union official, a paid director, or a paid consultant. Say yes and we can restore the reputation of this House."
ITV News Political Editor Tom Bradby said Mr Miliband's performance at Prime Minister's Questions was one of his "best" for a while.
MPs reject proposals for a ban on politicians holding paid directorships, consultancies or trade union roles.
Sir Malcolm Rifkind is to quit as an MP at the general election amid fresh pressure over cash for access allegations.