A MAN accused of raping and sexually abusing children has told jurors he can not be guilty – because he is impotent. Former social club treasurer Anthony Shackell conceded that he had been prescribed Viagra to treat his erectile disfunction. But he insisted he did not use it because the drug gave him a headache. And he indignantly told the prosecutor: “You have an evil mind.” Mr Shackell, now aged 81, is on trial at Reading Crown Court where he denies 16 charges of historic sexual misconduct towards children plus two, more recent, charges involving one girl aged just eight. The prosecution all…