Get Compatibility Report for Windows 10 in Window 7 and 8.1  

Did you get any error messages on this attempt when it failed?

There were a couple of small error windows that popped ip with a clang, I stupidly let them disappear but the gist was the same - Windows failed to install.......etc. Etc.

I tried it again with 1809 and got that blue popup I posted earlier, the same error code indicating it found a problem with the Boot process. I suspect my multi boot using EasyBCD 2.4 is bothering it somehow, which really should not happen as Windows Devs are quite familiar with that plus the fact that I've updated to 1709 with no problems. What I can tell you is what happens. The OS installs 100% and then asks for a restart.
It goes into a sort of standby mode with power still up and doesn't come out of that. I've waited 2 hours just in case. I'm then forced to power off and boot from scratch. It boots straight into my old Win 10 1709 and eventually that popup appears. I then have to clean up around 6 to 8 gigs of useless files using Disk Cleanup.
I do hope MS make pife easier for Win 10 upgrades before nexst January, otherwise I'll be forced to continue using Win 7 without Security updates.

I agree. It does sound like something with how you have dual boot setup may be causing it.

You may need to start fresh to get it to work.

I suppose I could uninstall the EasyBCD and rely on Windows boot. It simply enhances the control over the boot process allowing for any time delay you want or wait for user action, which I use, maybe that's a factor too.
I don't have time a.t.m. to try that but will as soon as I can.
Hitherto any install or upgrade of Windows has overwritten the settings anyway, so I'm pretty mystified over this.

Interesting quote from a response I got today over at MS: To All of You Getting With v1809 + - Here's a Quote - Windows 10 Forums