I clicked the "Upgrade later" option and immediately Windows 10 started downloading. I wasn't expecting this so abandoned the download.
Subsequently I got a message saying updates were available. When I had a look there was one recommended and six optional, one of the optional updates was the Win 10 upgrade. The Win 10 one was ticked for installation. If I had proceeded with the updates without checking first to see what the optional ones were Win 10 would have been installed.
Right now I don't see Win 10 as an upgrade, more like a downgrade for the time being. I don't want it yet. I'll decide when it's installed.
I wish MS wouldn't be so sneaky and insistent in trying to get Win 10 installed.