If you're installing from the ISO on a machine that has a formatted HDD, you will need a valid licence key to install.
This is the issue. In my case, I wanted to 'upgrade' to a 64 bit OS and it seems this can be done for free - once you've gone from 7 to 10 and it's all running. Odd that, since it's the complete wiping of the 32 bit that's so critical.
To me, this implied (past tense) that there must be a key hiding on that machine as the statement that a key would NOT be required was unequivocal. However, we have to go to a spare W7 machine to download the ISO.
The site is above, but I'm scanning letters from my dad in the war and can't be diverted too far off that project. One gets drawn into a world where he was sent on a course to learn about 'wireless'. It takes time to bring one's mind back to Large Scale Integration.