My problem seems solved. Robert from Dell pointed me at this link:
http://dell.to/2l3vK5S
This problem affects users with the DisplayLink driver and a Dell docking station.
Having applied the fix and used the PC over several days, the problem has not recurred.
One point I would add is when unistalling the DisplayLink driver you are asked if you wish to uninstall another program which depends on it. I replied yes uninstall it.