Mark,
i had a small issue with Ants last month had about 15 of the dirty ba$tards crawling around the kitchen floor. I got two tubs of ant powder and laced the outside of the house with it and make sure you get all your air bricks. Dont leave any food out or make sure it is sealed.
I then got some internal spray and sprayed it all on the skirting boards ect.
Touch wood it seems to have got rid of them.
You can get these products from (focus \ B&Q \ Wilkos)