THE principle of the separation of powers may be an 18th century concept, but it is essential to any modern democracy which values the rule of law. When it is breached, the proper administration of justice and due process is put at risk.

It was manifestly undermined during the phone hacking investigation staged by the House of Commons Culture Select Committee, particularly by Tom Watson MP, who, with the full benefit of parliamentary privilege, savaged the Murdoch family as a “mafia” whilst promoting his somewhat one-sided book Dial M for Murdoch.

Rebekah Brooks was also much maligned, even being portrayed as a witch on the cover of Private Eye, and it has been suggested, with good reason, that this manifestly prejudicial coverage made it impossible for any court in the land to convict her of anything.

This equally applies in the case of Michelle Thomson MP. Whatever she may, or may not, have done, she has not yet been convicted of anything in a court. Nicola Sturgeon may be right to distance herself from an affair which is proving to be particularly toxic, and the time may come when a charge sheet is drawn up, but for now it must be borne in mind that Ms Thomson is technically innocent, whatever her critics allege.

If she is guilty of any criminal offence, it goes without saying that she should pay the price, but it is for a properly constituted court of law to bring in the verdict, not an assortment of politicians and press commentators with various axes to grind.

It is also quaintly ironic that the Conservative MP who has reported her to the Parliamentary Standards Commissioner for bringing the House into disrepute as a result of her alleged profiteering activities (“Thomson reported to sleaze watchdog”, The Herald October 7) is Andrew Brigden, whose register of interests entry includes reference to the fact that he is paid £7,773 per month for reportedly working between six and 12 hours for his company, AB Produce PLC – let's just call it £1,000 per hour. I hardly think the moral high ground is his to claim, in this particular case.

David J Black,

6 St Giles Street,

Edinburgh.