Update.
My laptop has been getting very, very, slow and tormenting me with flashing ads, pop-ups etc on this site and others.
Last week I put my laptop into a repair shop ( I had it into another repair shop a couple of weeks but the guy was useless. Made my machine worse!), told the man what has been happening, and he suggested saving my data, wiping hard drive, and doing a complete rebuild.
"Carry on", says me.
I got it back yesterday and am mightily impressed.
The laptop is very fast again, and there is not an advert of ANY kind, on this site or any other. He installed Avast security and that may have helped. My computer knowledge is nil!
Fingers crossed for the future!