I have no intention of using my chimney again, What do I need to do to block it up permanently?

You should not block it up permanently, you should always allow the flue to breath. this can be done by closing in the fire breast, no problem, just leave a brass or chrome vent in the closure. cap the chimney pot with a capping vent cowl! venting your stack will prevent moisture and expansion of brick work during winter!! very important if you dont want your stack to deteriorate! kieran

When you block up the chimney ensure that you fit a rain guard cowl to chimney pot, to stop water getting in, and allow air circulation. Make sure there is a vent fitted in base of stack, you need good air circulation to avoid condensation and damp.