Commaster, thanks for the advice.
I launched as advised, certainly CPU goes to 100% and Code::Blocks shows as Not Repsonding. RAM never exceeds 46% of the available 16Gb, it sits at about 43% normally, and the disk is barely loaded. Only multiple instances of gcc showing up momentarily near the top of the list in the disk read column. I see some activity momentarily from anti-virus, etc., but it is just a spike not sustained.
I suppose I can rule out disk acces as the problem, unless the absence of disc activity is the problem.
There are two oddities in CPU usage during Code::Blocks launch as it is parsing the lexers, during that moment you see the program icon flashing on the taskbar. They are MS iType (Mouse and Keyboard Center) and Windows Driver Foundation - User-Mode Driver Foundation Host Process.
Interestingly, I've tried resetting the Code::Blocks Compiler options to defaults, I have the MingGW bundle installed. I see the very same sluggish behaviour on the laptop during the reset process with the CPU also going to 100% during this process. It automatically finds the MingGW install, but on the desktop the Reset to Defaults takes 1s and b arely loads the CPU, on the laptop it's a 10s long process with 100% CPU all the time.