A driver is weaving erratically down the road. He gets pulled over and the police officer asks him to breathe into a breathalyser.
The driver produces a letter from his doctor which says:" This man suffers from chronic asthma. Please do not make him perform any action that will leave him short of breath".
So the officer asks for a blood sample instead. The driver gets out another letter which says: "This man is a haemophiliac. Please do not cause him to bleed in any way".
Exasperated, the officer asks for a urine sample. Out comes yet another letter: "This man plays cricket for England. Please do not take the piss out of him".