The law on horse passports changed on 1 July 2009

All horses and ponies in England and Wales will need to have passports that identify them. The main purpose of passports is to ensure that where a horse has been treated with a veterinary medicine it will not be used for human consumption.
If you own a horse you must ensure that it has an up to date passport so that your horse can be identified, you could be fined up to £5000 if you do not have one. Your horse must be accompanied by its passport at all times, there are some exemptions to this rule which can be found on the DEFRA website
Adult horses that do not have a passport at present will need to be microchipped before you can apply for a passport. The microchip can only be implanted by a veterinary surgeon. Passports can be obtained from a number of Passport Issuing Organisations (PIOs) that are authorised by DEFRA
Foals born after 1 July 2009 will need to be microchipped. All foals will have to have a microchip and passport by 31 December in the year that they are born or by the time that they are six months old, whichever is the latest.
Trading Standards advise that you ensure that before you purchase a horse that the animal is as described and that you are supplied with a correct passport including a purchase invoice with details of the person bought from. Also ensure that you know if the seller is a trader or private sale as this would affect your statutory rights. If in doubt contact Consumer Direct
For more details on the changes to the law please follow the DEFRA link at the side of this page or see the Frequently Asked Questions (FAQs) below
National Equine Database
In the unthinkable event of your horse being lost, stolen or going missing on loan, the National Equine Database (NED) can immediately help you through its UK-wide lost/stolen register. Make sure its identification details and your owner details are up to date. (see 'Related Links' for further information)