they are libellous if they are printed, untrue, and defame the subject. It's got nothing to do with public interest. That defence is onlt valid for true comments impinging on a public figure's private life.
they certainly defame john and his colleague. point is, are they true or are they false?
theyre very serious allegations about this constituency's MP. Quite apart from anything else, the voters have a right to know if they are true or not, or at least what evidence the alledger has to offer.