Dodgy Tory MP Surely MUST Resign His Newark Seat.

A Panorama sting has apparently caught out a Tory MP taking a 'backhander' according to The Telegraph. I do wish I'd seen the programme.
Patrick Mercer no longer has the tory whip but surely cannot remain as an MP - or can he?

Incidentally, I do not think that the Tory Party would particularly fancy a by-election there!
(Is my mind letting me down but didn't Newark have a rather dubious Labour MP not so long ago?)