I\'m using Google\'s Geocoder to find lat lng coordinates for a given address.
var geocoder = new google.maps.Geocoder();
geocoder.geocode(
{
UPDATE: This answer may not be the best approach anymore. See the comments below the answer for more details.
In addition to what Pekka already suggested, you may want to concatenate ', UK' to your address, as in the following example:
Google Maps Geocoding only in UK Demo
Screenshot:

I find that this is very reliable. On the other hand, the following example shows that neither the region parameter, nor the bounds parameter, are having any effect in this case:
Google Maps Geocoding only in UK Demo with Bounds