All horses being exported/imported from the UK or France must hold a valid Passport
There are two types of recognised Passports:-
Those which are a Breed Society for horses with known breeding.
Those who offer a basic identity passport where breeding is unknown or unproven.
In France the Haras Nationaux control the issuing of passports for horses that fall into both these categories.
You can contact them through the Haras Nationaux site 
www.haras-nationaux.fr
Breed Societies who are approved under 92/353/EEC may now operate ‘cross border’ within the EU. e.g. they may issue passports for horses of the breed they represent for owners in all Member States. This particularly relevant if the horse concerned is legally eligible for entry into the studbook by virtue of having its parents entered there previously.
The Haras Nationaux still insist that these equines also be registered on the HN database. Equines Passport should be sent to SIRE, B.P,19231,Arnac Pompadour, Cedex, with the appropriate fee. You will get the original passport returned with an Carte d’immatriculation page added showing the animals SIRE number.
Basic identity only passport issuers cannot operate in other Member States.
They cannot issue their passports in another country (e.g. France) as these Member States have their own ID only issuers. In France it is the Haras Nationaux who issue them and these horses are then registered as being Origine Non Constatée (unknown pedigree equidae).
Therefore horses in France who are not pedigree equines and cannot be registered with a relevant Breed society in another member state must be issued a Passport by their own countries Passport Issuing Office,the horse is then registered as ONC (unknown breeding).
Microchip Identity (Transpondeur)
Horses in France must have a microchip as from 01/01/08 whether born in France or not, this will be necessary for registering with the Haras Nationaux. Fines of 450 € can be imposed to owners of equines found not to have a microchip.
In the UK it will be compulsory for all foals born after July 2009 to be microchipped. Each country has its own unique batch of microchip numbers, so it is easy to recognise in which country the animal was micro chipped.
Export Health Certificates
Health certificates are not required for equines transported between the UK and France because of the Tri-partite agreement between UK, France and ROI.
Returning to the UK
To keep up to date on rules and regulations it is advisable to contact DEFRA or view their web site http://www.defra.gov.uk/wildlife-pets/pets/index.htm which provides all sorts of information.
It is also a good idea to call a reputable horse transport company and ask them the rules. They do this all the time and will know exactly what to do and how.
Be prepared and plan ahead and leave time for arranging documents rather than be held back at the port.
