Stop US traffic affecting a UK Site bounce rate in Google analytics

Hi,

does anyone have any suggesitons on this. I have a UK site with good UK traffic stats, low bounce rate, good page views and time on site but the data is being skewed by traffic from US & Brazil which bounces straight out. I have indicated in the title and desc metas that this is a UK Service site and that helped a bit. Is there anyway to stop this unwanted traffic and improve my analytics..?