Ummmmm... that's a good question if you can get through to the payroll and admin department. My brother left a while back to move to the sister company and he is still having problems getting hold of his p45 and put it this way they still call him in for work even though he left over 3-months ago.
I'm thinking it's possibly the employers fault, so surely they should be molested, but the problem is proving it I suppose?