Passport is an ID system, it has a description and diagram of the horse, as of 2009, all horses wanting a new passport must be microchip, it contains the horses vaccine record, a record of other drugs administered (must be filled in by the vet who administers the vaccine), a section for you to sign if the horse has been administered any drugs that will make it unfit for human consumption. If it is a breed society passport then it will also contain full breeding and a history of ownership.
These details are collected by the passport issueing authorities (Normaly breed societies and a few others) and all information is put onto the national equine database.
It is illegal too sell a horse without a passport (but not illegal to buy it)
I personaly think passports are brilliant. It has virtualy stopped the indescriminate breeding of scrub ponies as now it costs more to passport them then they sell for in the auction ring.
I went to Beeston horse market several times over the winter and the number of them has dropped by 90%. Last time I went there was 2 maybe 3 scrub ponies (destined for the meatman from birth), when I went in 2007 you would get 40+ scrub ponies per sale!
Personaly I'm not sure I like being called a horse murderer by hysterical child.
I'll call her a cow murderer because to some religions cows are sacred and held in higher regard then horses have ever been.