A MERSEY MP has vowed to go to jail, rather than comply with a "nasty" new law requiring every detail of his “second job” to be revealed.

Birkenhead MP Frank Field pledged to defy the crackdown – introduced in the wake of the expenses scandal – which he condemned as absurd, illegal and doomed to fail.

The Parliamentary Standards Bill, which cleared the Commons last night, requires every MP to reveal exactly how much they earn from private-sector work – as well as the hours they spend doing it.

And it threatens any MP failing to properly declare their “extracurricular earnings” in the Commons register with a one-year jail term.

Mr Field, who is a paid director of Medicash, a Liverpool-based mutual health insurer, said he was happy to reveal his earnings, but not the hours he worked.

The Labour backbencher described the idea as "demeaning and impractical" because, in his work for Medicash, it was impossible to calculate when his job as an MP ended and his outside work began.

He explained how he recently held a meeting to discuss a village's plan to drive down power prices by bidding collectively for gas and electricity – an idea also of interest to Medicash.

And he asked: "How do I time that activity? When was I carrying out my MP role and giving advice, and at what point should I have clocked on for Medicash?"