Thank you kiko964 for your suggestion about iotop, It looks to be a very useful program I normally run System Monitor and Logs permanently as the second and third programs that I start, (Navigator is number 1). I have already installed iotop and it looks as if I should start it as number 4.
I now suspect I have a hardware problem as since entering my first question I have observed other symptoms. I have noticed a key bounce problem for some time and yesterday I swapped in a new keyboard but this made no difference. Sometimes I use F11 to swap in or out of full screen mode and the screen swaps one way and then swaps back. This is so ubiqutous that sometimes I have to press F11 5 times before it works. Also ocassionally I get four characters typed instead of one. Another sympom is irregular mouse movement and slow keyboard input even when there is no noise indicating HDD operation.
Maybe the laptop is becoming flakey, it may be old age or it may be something simple like dust in the heatsink. It is out of warranty now so I can open it and clean the heat sink and get rid of dead cockroaches and their droppings. It gives me the creeps every time I see a German cockroach (that is the small type) trying to crawl into the space between the display and the keyboard, time to reapply poison gas.
To answer your question the computer is an Asus Vivobook X540M.
Keep social distancing and wear a mask if you can get one. Masks have an protective effect and the protective effects of mask and social distancing shoukld multiply together. The reason that so many are advising against masks is that there is a shortage and medical staff can’t get a sufficient supply.
Regards, The Evil One.