Posted: 10/02/2013 at 18:07
Have you any plants in pots which you put outside during the summer and bring in for the winter? Ants often take up residence in the pots, particularly in wet summers like the last one - ants prefer dry soil and will seek out pots etc which are above the water table.
If you have any such plants on your windowsills I suggest you stand them in a washing up bowl full of water for a few hours and let them have a really good soak until the surface of the soil is wet - I bet the ants come out! You'll have to squidge them then