My thanks for your comments. The hard start is now solved. I pulled a glowplug, saw a blob of carbon around the tip (like a match head). When this was removed and cleaned with EGR cleaner and checked for heating ability the car now starts fine. I have cleaned the other glow plugs. In this case the glowplugs would test OK electrically, but not present a red hot tip to the fuel.
This all makes sense. However The glow times still don't relate to the coolant temperature (workshop manual table). My glow time(lamp) for 5 deg C is only 3 secs, which seems a bit ridiculous especially if the heat has to get through some carbon. Any other comments are welcome