Nick,
if this is the first time you've had them (bearing in mind that I
don't have the first clue how long you've been in your current house),
then the chances are you won't see them that frequently.
For some reason in my house we used to have them as far too
frequent guest, but the filling of some old crumbled mortar has evicted
them from their old summer holiday home.

Personally, check back when the weather gets warmer and see if there's
the beginning of a new nest (it will be a very small little paper mache
ball), if there is then perhaps investigate some of the various
chemical solutions. Generally, the nest you have there now will be last
years nest and will be completely vacant. Follow the other posters
advice and remove it with a thick plastic bag and if you're really
worried then freeze it over night,

If there's no new nests over this summer then to be it's probably
easiest to just forget about them and check back each year.
Hope this is of some help.

Seri