I found quite a lot of duff data appearing in my incomplete database of UK postcodes, so thought I’d better filter out some of the rubbish. So the obvious thing to do was figure out which latitude and longitudes weren’t in the UK and stop them being put into in the database in the first place and also delete the ones already in there. There are definitely better ways of achieving this but my simple solution seems to have done the trick. First check the latitude is greater than 49 and less than 61, then check the longitude is greater than –12 and less than 3. It’s not perfect but I think it’s probably good enough for many applications.