Normally when the item is confiscated you should be issued with a notice stating what will happen to the item:
1 - Carried by the airline to your destination.
2 - Held for thirty days at the airport and then disposed of.
3 - Disposed of by BAA.
If you have this form call BAA at the number printed on it or call the switchboard at 0870 000 0303 to see if they still have it.