vauxhall zafira 04 diesel white smoke from exhaust?

Is the engine losing coolant? If not it may just be coolant lying in the exhaust which will reduce over a few miles.If it is then the head has not been fixed properly.
Either way you will probably need a new cat and lambda sensor(s).
Did you pressure test the head and check for flatness before refit?

sdsdsds
August 2009