Anyone who wants to train a horse to run at any of Britain's National Hunt courses must have a licence to do so from the Jockey Club.
There are currently about 700 licensed trainers in Great Britain.
The elite trainers have first-class facilities with state-of-the-art equine pools and blood-monitoring equipment.
But many others have much smaller establishments - sometimes just a stable in the garden.
The latter are likely to be what are known as permit holders, which means that they can only train horses for themselves and their immediate family.
Permit holders often have just one or two horses although there are exceptions - Norman Mason, trainer of 2001 Grand National winner Red Marauder, had about 50 horses.
Fully licensed trainers can train horses for anyone.
In 2001, four trainers had more than 100 winners. All had big yards, especially Martin Pipe, who has over 200 in his Pond House Stables.