I have a copy of an older installer on my hard drive.

google throws up some options:

for opera 35: http://filehippo.com/download_opera/tech/66536/

for opera 42: https://www.softexia.com/windows/web-browsers/opera-42

I am back on version 42 and have disabled auto updates by renaming the autoupdate executable in the opera folder in program files. Will wait for the next version to see if they have fixed it

YES - I can confirm that this is a problem in the latest version of opera - glad to see I'm not the only one.

I just proved it by going back to version 35 - all ok, then it updated to version 42 - still OK then updated again to 46 and the problem came back.

I noticed it on a couple of news sites that I read everyday. Try the Guardian and you should see that the font's resolution is terrible: https://www.theguardian.com/uk