Zara Phillips will have one eye on the 2012 Olympics when she competes in the Blenheim International Horse Trials, which get under way today.

The 27-year-old daughter of the Princess Royal, who won individual gold for Great Britain at the 2006 World Equestrian Games, suffered the disappointment of missing out on last month's Olympics in Beijing after her horse, Troyton, was injured.

This week, Phillips rides Tallyho Sambucca, who is seen as a prospect for London in four years time.

The field also features William Fox-Pitt and Mary King, two of Great Britain's bronze medal-winning team from Beijing.

They also have rides which are seen as future prospects.

Fox-Pitt, fresh from recording a one-two at Burghley last week, has three entries in Navigator, Seacookie and Kaleidoscope, while King is aboard the half-sisters Kings Fancy and Kings Temptress.

Around 50,000 spectators are expected at the event, which features two days of dressage followed by the cross country on Saturday and the showjumping on Sunday.

The going was yesterday described as good to soft.