Controversial proposals to pay MPs with outside interests less than “full-timers” are set to create a new row as Parliament tries to recover from the the expenses scandal.

As Gordon Brown and David Cameron pledged to lift the blackout on expenses for future years, it emerged that the Senior Salaries Review Body (SSRB) will look at the option of differential pay scales for MPs.

The move would disproportionately affect Conservative MPs, far more of whom have second jobs than members of Labour or Liberal Democrats.

The plan emerged at a meeting of the Commons Public Administration Committee, at which Bill Cockburn, head of the SSRB, suggested that MPs were underpaid by 10 to 15 per cent.

But when Tony Wright, the committee chairman, asked about differential salaries for full and “part-time” MPs, Mr Cockburn said that was something the review body would look at. The committee, which will reform the expenses system, is considering whether MPs should be allowed to have outside interests, and it seems certain to consider the idea of differential pay if put forward by the SSRB.

From July 1 MPs will have to disclose how much they earn from outside jobs and the amount of time and commitment it takes them to earn it.That requirement is leading MPs to scale back their outside commitments.

Mr Wright told The Times last night: “I was surprised by what he said. It makes an interesting contribution to the current debate. I suppose there might be a certain logic to paying full-time MPs a full-time salary and part-time MPs a part-time salary.”

But some Conservative MPs would see such a move as politically motivated and others voiced doubts last night.

Ann Widdecombe, one of the candidates for Speaker, said: “I think it would be very, very, very difficult to define what a part-time MP is . . . because any MP who’s a minister is also doing something else.”

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