The British eventing ace will be joined at the event's 40th anniversary by fellow Olympic silver medallists Zara Phillips and Nicola Wilson.
Also appearing on their home turf will be other British stars Pippa Funnel, Piggy French and Oliver Townend.
New Zealand will also be strongly represented - Jonathan Paget, Jonelle Richards, Caroline Powell and Mark Todd have confirmed their appearances - while France have also travelled in numbers and with quality: Donatien Schauly, Sydney Dufresne, Cédric Lyard and youngster Astier Nicolas will all ride.
All horses passed a compulsory veterinary check on Wednesday and are fit and ready to compete in the three classes to come over the next four days.
First up on Thursday is the dressage which will roll over to Friday, with the cross country scheduled for Saturday and finally the jumping on Sunday.
- Sports & Recreation
- Zara Phillips
- Jonelle Richards
- Caroline Powell
- British eventing
- Jonathan Paget