Alistair Darling is used to dealing with much bigger figures: the chancellor who announced he was borrowing £175bn this year apparently failed to notice the £668 expenses claim that has set a time bomb ticking under his political career.

Mr Darling will learn later this week - possibly as early as Friday - whether he will become the latest casualty of the expenses scandal that has gripped Westminster for the past three weeks, as Gordon Brown plans a cabinet reshuffle.