Are you totally sure you are not still running the old flash version, which has some issues at present, but sorting out the main tester issues for the few who seem to be having issues.

What browser in Windows 10? Do you have Edge Creator update installed?

As MrSaffron says re the flash test. If you are using a bookmark/favourite to get to the test you possibly need to replace the link with one to the new one. It's probably the same but starting with https: not http:

Trying again this morning when rather more awake. Having reread all of yesterdays responses I realised I should have tried Firefox as well as Chrome (my usual) It worked perfectly well. Sorry to have wasted every one's time. Why Chrome objects to it I can't guess but maybe they will sort it in due course.

Just checked again on Windows 10 using edge and logged in or not the test works and result is saved when using http://www.thinkbroadband.com/speedtest