FOR years Zara Phillips, Britain’s champion equestrian, endured a tense relationship with her father as he put her under relentless pressure to succeed. But now, as both prepare for the Beijing Olympics, it is he who is under scrutiny.

Mark Phillips, a former gold medallist who now coaches the US eventing team, has been forced to defend himself after accusations that courses he has designed are unsafe.

In the past 18 months there have been two deaths on cross-country courses that he designed. Last month Darren Chiacchia, a US gold medal prospect for Beijing, was left in a coma after crashing over one of Phillips’s fences.

The incidents have split the riding community. Top riders blame overenthusiastic amateurs for taking too many risks, while amateurs say courses are being designed beyond their skill level for the elite riders.

After internet bloggers called for his sacking from the US Olympic team, Phillips released a statement insisting that his courses were safe. “I have been dismayed by the reaction of many in the eventing community . . . We can never eliminate bad days. We acknowledge that we are involved in a risk sport. If you participate in such a sport, accidents will happen,” he said.

Denny Emerson, former president of the US Eventing Association, said top course designers needed to take responsibility.

“Course design has become a game of cat and mouse between designers and riders. The designers make them tough, so riders learn how to do it, so the designers make them tougher again,” he said. “They have pushed each other to the brink of danger. It is unfair to blame Phillips for this trend alone, but maybe it will do some good because he is so well known it will start a debate.”

Eventing, which has been an Olympic event since 1912, was originally designed to test the ability and endurance of military horses. Riders compete in three events - dressage, show jumping and cross-country.

The cross-country phase is the most dangerous, as horse and rider are required to clear up to 40 jumps. They are penalised if the horse balks at a jump, falls or if their time is slow.

Phillips’s courses are known for being challenging. His designs are characterised by obstacles grouped closely together, making it hard for horses to build up momentum.

Carol Ogden, president of the Florida horse trials association, a club for amateur riders, has ridden Phillips’s courses at Red Hills in Tallahassee, Florida, where Chiacchia was injured, and at Florida Horse Park in Ocala, where two riders died. “I didn’t like them at all. At Red Hills you have to slow down all the time . . . I couldn’t even complete one of the courses. I think riding a horse should be about galloping across country at full rhythm and having the jumps disappear under you,” she said.

Phillips, nicknamed “Foggy” in royal circles for his supposed lack of intellect, married Princess Anne in November 1973 but the couple divorced 19 years later.

He forged his reputation as a course designer in Britain where he won plaudits for his cross-country jumps at Burghley, in Lincolnshire, and the annual event for Anne at her Gatcombe estate in Gloucestershire. But in September 1999 Simon Long, a Wiltshire-based rider, died at Burghley after his horse crashed over a water jump.

The fatality was one of five eventing deaths in Britain that year and led to pressure to make courses safer. In response, organisers developed “frangible pins” enabling rails to pop out when hit by a horse.

However, although the pins have been available since 2001, they are still used on only 4% of obstacles in Britain. In August 2006 Sherelle Duke, a friend of Zara’s, died on a course designed by Phillips after her horse somersaulted over a log jump and landed on top of her.

Phillips joined the US Olympic team in 2000, but has been a course designer and safety adviser in the United States since the early 1990s. He said yesterday that the safety of athletes and horses was always his “top priority”.

Additional reporting: Anna Mikhailova