Well, of course I knew the answer as it's Enid Blyton.Lochee-born artist William Lindsay Cable is known for his cover illustrations for which English children's author?
It then gave some further information.
How did I never know this? (Lochee is an area of Dundee, where I've lived all my life.) The Dundee Advertiser was later taken over by The Dundee Courier and is still published today.Cable, the son of a cabinet maker and undertaker, was born in 1900 and worked for the Dundee Advertiser before building a career in London. He illustrated many of Blyton's boarding school stories, including the St Clare's series.
I wish I was still at work so I could go to the Local History department and find out more!