Headley Britannia, stable name Brit, is a mare competing at the highest levels of the equestrian sport of eventing. Relatively small for the sport, her jumping ability, manoeuvrability and willingness propelled her to the top of the sport.
- Foaled: 1993
- Color: Liver chestnut
- Markings: Star
- Height: 15.3 hh
- Pedigree: by Jumbo, out of Alan's Bambi
- Breeders: Mike and Betty Hounsell, Headley Stud
- Rider: Lucinda Fredericks
- Owners: Lucinda and Clayton Fredericks
Headley Britannia is by one of the top eventing stallions in Britain, Jumbo, who first competed at the Advanced level with Andrew Nicholson as a seven-year-old. The stallion has been a top producer of eventers, dressage horses (his get have reached Prix St. George), and Grade A show jumpers.
Headley Britannia's greatest accomplishments include a win at the 2006 Burghley Horse Trials, the first mare in 33 years to do so, and a win at the 2007 Badminton Horse Trials, the first mare in 53 years.  She came third at the 2006 Luhmuhlen Three Day Event, a great accomplishment after having taken a fall the previous year on the cross-country and after which contracted a virus which nearly killed her.  She was an alternative to the 2006 World Equestrian Games, but when not called, was switched to the Burghley Horse Trials.
In 2007 her owners Katinka and Neil Thorburn gifted her to her rider, Lucinda Fredericks. After winning Badmintion she went to stud for embryo transfer.  Summer 2007 - Having undergone embryo transfer, Brit's embryos were transferred to two surrogate mares, and are now in foal to what are believed to be the next progency of British Eventing. The foals, by world renowned stallion Jaguar Mail are expected to be foaled in 2008. 
The first of Brit's two foals was born in April 2008, a chestnut filly with a white star. Fredericks later confirmed that the second foal had been born in May 2008 this one being a dark bay colt. Strangely the foals resemble much like their parents, the filly, Little Britannia, is chestnut with a white star like her dam, and the colt, Britannia's Mail looking remarkably similar to his sire Jaguar Mail, dark bay in colour.
- Headley Britannia rules over land as well as water - article in the Independent