Google has started popping out ads from the side when I go to certain web pages which covers about a quarter of the webpage. I find no cure by searching Googles ad preferences page.
Is there a way to switch to a different search engine in Opera ??
Most likely those are not google ads, but some rogue software on your machine. Try to disable your extensions; if this doesn't help, check your machine with ADWCleaner ( https://toolslib.net/downloads/viewdownload/1-adwcleaner/ ).
Yes, I think something bad snuck into my machine.
The reason I wanted to change the search engine is because it was only doing it with Opera and only Google. I did a system restore which seemed to fix the problem then saw Donq's message and ran ADWCleaner which was good advice.
Now I'll see what happens.