UK Car Repair: Expansion tank losses???, vauxhall corsa, head gasket

Question
I have a vauxhall corsa 1.4 gls, It had a shunt recently and i had to replace radiator, wing, bumper and bonnet, after this it has been losing jacket watersomewhere, there are no noticeable leaks from radiator pipes but the engine oil is emulsifying, would this point to a problem with the head gasket? Any help would be appreciated and a approximate cost for replacement gasket??

Answer
Water in the engine oil is serious and the car should not be driven.  It could be a head gasket, but it seems odd that it happened after the collision.  It is more likely that something cracked, perhaps the timing cover/water pump flange etc,  Prices I do not know, but it is essential you get it seen to ASAP.  I would assume it was somehow related to the "shunt"!