Never try to take a star nut out the same way the it went in (i.e. through the top). They are designed to withstand large forces in this direction so will damage your forks. What you will need is a rubber mallet and a couple of extender bars for a ratchet driver. This is how you do it:
1- Place the bottom of the forks on a solid surface (the floor generally works well).
2- Put the shortest extender bar in the steerer tube so it sits on the star nut, then smash it with a mallet, this will get it moving).
3- Repeat step two with until the top of the steerer and top of the extender are flush, then change the size of the extender and repeat.
4- It will eventually just pop out.
Trust me, it is the Halfords way - If you don't have the correct tool, smash it with a hammer.
Hope this helps.