Hi Ulf and others,
Problem solved! It was the tracking program “Prey”. It was making the CPU run at around 30% continuously and for some reason it prevented Dorico (and Cubase) from operating with multiple processors. Both programs work fine now and CPU usage is down to a few percent (and the battery of the laptop lasts much longer!)
Now I can compare Dorico and Sibelius as I’d hoped to do in the first place!
Many thanks for your help.
Philip