Works like a charm after the restart. Thanks very much. Do you reckon this issue will recur?
JakeRawlins, not sure whether or not this will completely resolve the issue but I've turn the fast start-up off (Control Panel\All Control Panel Items\Power Options\System Settings). So far so good - no more freezes 

Fast Startup combines elements of a cold shutdown and the hibernate feature. When you shut down your computer with Fast Startup enabled, Windows closes all applications and logs off all users, just as in a normal cold shutdown. At this point, Windows is in a state very similar to when it’s freshly booted up: No users have logged in and started programs, but the Windows kernel is loaded and the system session is running. Windows then alerts device drivers that support it to prepare for hibernation, saves the current system state to the hibernation file, and turns off the computer.
When you start the computer again, Windows does not have to reload the kernel, drivers, and system state individually. Instead, it just refreshes your RAM with the loaded image from the hibernation file and delivers you to the login screen. (Ref. The Pros and Cons of Windows 10’s “Fast Startup” Mode )