The UK's horse passport rules have been tightened up from the begining of July 2009. The horse's owner or keeper is responsible for making sure that each horse has a passport, and that it is available for inspection at all times. You don't need to have the passport with you when the horse is grazing or being moved on foot - but you do have to show it to an inspector within three hours of being asked.
With very few exceptions, all horses have to have a passport. Both the owner, and the main keeper, is responsible for making sure the horse is correctly identified - but only the owner can apply for the passport.
The big change is that to be issued with a passport now horses must be microchipped. As a consequence, the diagram (silhouette) of the horse is no longer compulsory. However, many breed societies and passport issuing authorities still require a silhouette at this time.
For more details see: