The money could be donated to an array of charities including the Tearfund, Chest Heart & Stroke Scotland, the Prince’s Trust, Mary’s Meals, Save the Children and thousands of small Christian and community groups which have been helped by the Souter Charitable Trust.

The Scotsman reported that Sir Brian made the surprise announcement yesterday that he was donating 28% of the shares from Souter Investments.

George Young of the Charities Aid Foundation (CAF), an international charity which aims to promote a culture of giving worldwide, said Sir Brian’s donation had come at a time when the charity sector was undergoing a “perfect storm”.

Sir Brian also revealed its portfolio had outperformed the stock market by 55% in the past 12 years and said it is seeking new investment opportunities.

The firm’s portfolio, excluding Stagecoach, increased in value by 9% per annum from December 2006 to March 2019.

Sir Brian said: “Given the excellent performance of Souter Investments, I have today gifted 28 per cent of its shares to The Souter Charitable Trust; I estimate that the value of this shareholding is £109m.

“The Souter Charitable Trust has donated more than £98m to 13,000 worthwhile causes over the last 13 years and this gift will allow it to continue this important work.

“Despite the uncertain political and economic times facing us all, our portfolio is in good shape and Souter Investments has the liquidity to continue investing through the cycle.

“I remain positive in the ability for canny investors to find value in the coming years and hopefully Souter Investments can continue to be one of those investors.”

George Young added: “Something we’ve seen in Scotland and the rest of the UK is that the number of people donating has gone down. But the amount being donated is staying the same.

“So, we have fewer people donating more. We are carrying out investigative work to try to find out why some people appear to have lost faith in some charities. Charities are experiencing a perfect storm right now.”