I have been reading a book about the many uses of vinegar, and one of them was to get rid of ants. We tried it in the house last year, putting it down cracks where we had seen them, and putting it all around the outside of the house - and it worked!
No ants in the house since, and we have done it all again this time.
However, we are having a lot of trouble in the greenhouse, so have tried it in there. No ants up to present, but watch this space!