From their website:
From the 14th May 2010 until the 28th May 2010 you can get a free pack of HOF43 Armoured Sentry Robot, worth £3.50, for free paying nothing but the flat rate postage worldwide.
You can place as many orders as you like. But you may only place one free pack into each order.
We will not honour orders with more than one free pack in them. You can add any other items to your orders as normal and still claim a free pack.