What I normally do is nothing at all. I often get them in my garage or roof spaces and so do most of my neighbours and we just let them get on with it. Sometimes the nest is the size of a tennis ball and sometimes the size of a football but they dont do any harm and in winter you can remove the nest if you want to.

Not ant powder, but there is a special wasp killer powder that you can use. It is puffed around the entrance of the nest in the early evening and the wasps take it inside as they return for the night. However, this is still a chancy operation if the nest is not easily accessible.
If the wasps are not causing you any problems I would do as Inverglen suggests and leave them alone. In winter the wasps die and the nest can be removed or not as you choose. They don't use the same nest twice.

Thanks for that folks - panicked when I first saw the size of the nest, bigger than a football. The wasps were all coming in my bedroom window from the garage roof. I couldn't access the entrance as too high up to reach so Pest Control came today.

Interesting that the wasps never use the same nest again isn't it, but I guess if they die off in winter........