The changes occured at last Monday’s SNP group annual general meeting - and the veteran councillor who is a former head of history at Cumbernauld High School has not not indicated any intention to withdraw from elected office prior to next year’s elections.
However Councillor Johnston - whose wife Cathie is also a councillor - says he voluntarily gave up the leadership.
And he revealed this was quite simply because his own personal circumstances have changed in the midst of a gruelling few months.
He stated: “In the week prior to the AGM of the SNP group, I intimated that I would not be seeking re-nomination as group leader.
“Last November I spent a full month in hospital with a recovery period thereafter.
" I also suffered from a very close family bereavement in Cumbernauld at Christmas.
"We spend a lot of time with our two young grandchildren. All these factors led me to my decision not to re-stand as group leader.“I have great confidence in the younger members of our 29-strong SNP opposition Group and have no qualms about handing over to them."
Councillor Linden whose ward is in Bellshill has been replaced at deputy level by Wishaw councillor Fiona Fotheringham.