janner sent the card to detective after learning he would not be charged .
christmas card even invited retired kelvyn ashby to dinner at parliament .
former policeman said he was appalled by the labour peer 's note .
officer says superiors forced him to drop inquiries into alleged sex abuse .
four medical experts who examined the peer did not all agree on the nature and extent of his dementia , as outlined by mrs saunders ; .
janner 's own barrister was surprised he escaped charges in 1991 , and suspected attempts to influence the prosecutors ' decision ; .
the director of public prosecutions in charge at the time said he could not even remember seeing the politician 's file .