We are witnessing a spate of inappropriate ex turpi causa defences. Under our common law the courts have a policy that is intended to prevent a criminal from recovering compensation where the loss or injury complained of is inextricably connected with and caused by his own criminal act; its common sense really. This defence is commonly associated with the Latin maxim: ex turpi causa non oratur actio; also, more rarely with ex dolo malo non oritur actio. In recent years ex turpi causa tends to be routinely cited by defendants whenever a claim is associated with some kind of criminalily.
The ex turpi causa policy is not about punishing miscreants. Criminals enjoy the same civil rights as the law abiding; we abolished outlawry a while ago.
Ex turpi causa seeks to avoid the perversity of compensating someone for the direct effects of their own crime. So in Delaney v Pickett Pickett  EWCA Civ 1532 the defence failed to prevent a passenger (who happened to be involved in drugs dealing) from suing his associate when he injured him through his negligent driving of the vehicle that was transporting their stash of marijuana to the next deal. Their criminal activity was not the cause of the accident; rather, it was the defendant’s negligent driving.
However, in Joyce v O’Brien and Tradex 2013 EWCA Civ 546, the Court of Appeal upheld this defence against a thief who fell off the back of his uncle’s get-away van. Joyce had been holding on to a set of ladders that he and his uncle had just stolen, whilst at the same time trying to cling on to the back the van as it sped off from the scene of the crime. He fell off when his uncle executed a sharp turn at speed and sadly Joyce sustained grave head injuries. The Court of Appeal rightly took the view that ex turpi causa applied here.