There are some genres of newspaper story that never die. Among them are sightings of Lord Lucan, public moralists discovered in adultery – and foolish MPs being caught out offering themselves for hire to undercover hacks. A fine example of the third of these broke yesterday thanks to the situationist campaigning group Led By Donkeys, who started out as Brexit-bashers but have expanded their remit to the broad-brush embarrassment of MPs. You’d think,