Does anyone have any information on optimum height for lcd flat screens, I have been advised recently that th top of the screen is not suitable viewing level for flat screens, any info or sites would be appreciated.

The height is entirely dependent on the task and apptitude of the individual.
If the employee has ppor keyboard skills and has to look down at all the time, then the screen should be down there too. OK for a touch typist, although height should be optimised to ensure the eye-level is on the active section of the document or application, and not on the frame of the screen or myriad toolbars that might be open.
This should certainly not be a hard and fast regimented rule, and modern screens will afford sufficient height adjustment for the individual.
The above discussion in a Personal Computer context. The Regs also apply to process control rooms, TV editing, CCTV centres etc. which might involve a whole bank of screens on a wall or panel,

It does depend on the height of the user, and the outcomes of their DSE self assessment. There are loads of monitor stands on teh market so that you can get a screen to the right height quite cheaply.