It starts easy but when the engine revs drop slightly it runs lumpy for a few seconds and some white smoke I've changed the glow plugs any ideas

White smoke is water, so that is either water vapour out of the engine and exhaust being burnt off if the temperature is cold, (perfectly normal), or water from the coolant system, are you ‘loosing’ coolant?

No mate never lost any water but it only does it on the first start of the day

It is perfectly normal then, the white smoke (which is actually steam) should clear when the car his up to normal running temperature.