My theory on what happened, but I'm no expert.....
We got a few ants coming in from wherever the nest is/was and for several days, before the 'party'. We began putting ant killer down, which attracted even more from the nest, hence the 'ant party' yesterday evening. This morning we were still spotting odd couple around. Since then, not a single one to be seen and no dead visible ones.
What worked, for future reference, was - 3 parts icing sugar; 1 part borax, mixed to a paste with water. Dip cotton wool balls in the past and put them where I saw most ants congregating. It worked much better than Nippon ant killer and better than the dry mix left around in plastic milk bottle tops.
Thanks,
I'll try that tomorrow, I thought my mix was working, but they haven't touched it after that little bit yesterday, tried another 2 types of mixes and neither worked.
Will try your trick with the cotton wool balls