BINGO!!!!
Thanks for the link Albeig - went into the device manager and updated the driver for the ACPI PC within the "computer" settings - a quick reboot and it's all sorted. Back to a nice smooth online game with a decent FPS of 90+.
As to why it happened
who knows - one of those PC things I guess
illepall .
Perhaps we could get the devs to make a sticky link to this apparent "freezing" fix?
Thanks to everyone who posted and offered advice - your time and efforts are much appreciated.