I had the same problem 3 years ago. My garden is one giant ants' nest and I'll never be able to get rid of them but I found they were in the house too, hundreds of them. I discovered that they were coming in through a tiny gap between the skirting board and the wall in the dining room.
First I put ant powder down but it didn't kill them all off so I laid a little bit of sugar on the carpet next to the skirting board. That brought them out in droves and I just stood by with the Dyson hose and sucked them up. When I'd got all the ones that had appeared I pushed ant powder down the crack with a knife and then used Polyfilla to seal it up. I haven't had any in the house since then.
