no I wouldn't really send that email. I thought about it and realised it was impossible. But the only other two possibilities that I can see (are there others?) are:
1 - put up with it, spend time and money on a night out you didn't want and miss out on the one you did want
2 - tell people (though maybe indirectly through an intermediary), who have already been told they can come, that they can't, which is obviously rude.
For a crazy moment I thought that 3:
3 - let other people go out with whomever they want, but don't go yourself if you don't want to
was actually less rude. Logically I think it is, but practically I can see that you can't actually tell people you are doing that once you have booked a night out (arguably you could get away with it if someone else booked it? not sure? what do you think?)
Does anyone think that option 2 is less rude?
If not then you are stuck with 1, which isn't fair