A plan to threaten MPs guilty of expenses scams with up to a year in jail was in danger of backfiring after lawyers ridiculed it for – again – offering parliamentarians more lenient treatment than those they represent.

Transparency International, the anti-corruption group, said it would be a “clear abuse of office” for lawmakers to pass rules that would allow them to escape with just a tenth of the maximum jail time imposed on members of the public involved in fraud.