After talking with Apple support I have done the following as requested;
However that didn't resolve the issue, so I was instructed to test in safe mode to ascertain if it's driver or possible hardware. The same issue appears in Safe mode so it's hardware.
This is a known OSX bug. Let me find the link for you on this.... http://support.apple.com/kb/TS4135
You need to complain to Apple to get this fixed. The more complain, the more they're likely to fix it.
Many thanks for this info, but I am surprised that Apple didn't suggest this if they know it's a known fault! I shall monitor it now and see if it reoccurs but I have disabled automatic logout and just set a password for screen saver and sleep.
I have clicked "this has helped me" as you have done more than Apple, so let’s hope this resolves it; especially when it’s only two weeks old! If the solution works I shall click "This solved my question"