I subsequently managed to reboot through a single user command line using the fsck disk utility to repair the disk.
Once up and running again I ran the disk utility to repair the disk and permissions.
This was where I got the following issue...
Permissions differ on “Library/Internet Plug-Ins/JavaAppletPlugin.plugin”; should be lrwxr-xr-x ; they are drwxr-xr-x .
I repaired the permission and backed everything up on a 1TB My Passport through Time Machine.
The MBP crashed again, while watching a flash video on Safari.
Again it would not reboot normally, to the recovery partition or to the backup on My Passport.
I used fsck again to repair and reboot successfully.
Running disk utility again I got the same permission difference again.
I also still get a flickering picture on video in Safari or chrome and my whole experience is now quite sluggish.
Finally, I went onto App Store and found in my purchases that OS X Mountain Lion has a 'download' rather than 'installed' button next to it, while About this Mac tells me I'm running 10.8.2
Do you think I need to reinstall 10.8.2?