No, the progress bar rarely goes to 100%, except, if I remember, when upgrading Android 5 to 7, which I have done at least twice now. I downgraded and then went back in steps as advised by pcristi, but neither of his 2 ways of getting to 2.0.3 worked.
I am very computer literate, so all my hidden files and extensions are always on, and the correct .zip file is always used. 
When I re install custom or official 2.0.1 the progress bar only gets to 70 - 75% but the system then boots and runs normally. It is only when trying to go to 2.0.3 that I get the problems.
Do I definitely have a UK version Q5? I think so, as I have 5GHz wifi available (though not used) and 8GB memory, and, I assume, it would not run 2.0.1 when installed.
Is Android 7 fully installed? Can't answer that for sure, maybe there are diagnostics available to understand where the incompatibility lies, or what is blocking the 2.0.3 install. I am even using NTFS formatted usb drives as told by pcristi, but fat32 drives result in the same behaviour.
All my normal end to end fault finding analysis are not finding the problem, can't think it is hardware, so O/S problem seems likely.
If all else fails, I wonder what, if anything, I am missing by not being on custom firmware 2.1.1, which would be the ultimate aim?