Blyth Tait, Olympic three-day event champion and favourite to take the Pedigree Chum honours at Burghley this weekend, has threatened to withdraw his top horse, Chesterfield, from the competition following dressage marks that left the New Zealander "extremely disappointed".

"I did a competitive test, but it's not going to be a competitive mark," he said after his pathfinder test with his Atlanta Olympic team horse. "I feel I was victimised by being first to go. There's a discrepancy of 27 marks and if he's not in with a chance at the end of the dressage I'm going to withdraw him."

Tait was particularly displeased with the marks from British judge Angela Tucker, who was substantially lower than her two counterparts, Dr Bernd Springorum and Barry Roycroft. "She was way out of sync with the other two. If she realises and changes her marking later on then it's a waste of time coming here. Now the horse has only a place chance at best."

Chesterfield was also drawn number one at the Atlanta Olympics when Tait led the New Zealanders to the team bronze before going out to win the individual gold with his second horse Ready Teddy. He is now being saved for a crack at the world title in Rome in November, but Chesterfield, who has had two top five finishes at Badminton, was Tait's main hope for the Burghley title, which has so far eluded the 37-year-old.

Tait's outspoken reaction to his marks has resulted in his marks being reviewed by both the ground jury and appeals committee. Tucker declined to comment but Hugh Thomas, chairman of the Burghley appeals committee, has requested that all tests with a differential of either 10 per cent or 25 marks between the top and bottom marks should be reviewed.

No alteration can be made to Tait's score, however, and any review of the marks will serve only to improve the standard of judging.

Tait is hoping that his second horse, Aspyring, which is drawn six from the end this afternoon, will benefit from this anomaly in the way that his stablemate has been handicapped.

All the riders, however, are agreed that it is unlikely that the dressage will be too influential at Burghley; most believe the crosscountry track to be the biggest they have ever seen.

Ireland's sole runner at Burghley, Austin O'Connor, was not unhappy with his mark of 67 pen alties for overnight 22nd with the mare Simply Rhett.

Ireland's only autumn threeday event, which was due to be staged at Necarne Castle in Irvinestown, Co Fermanagh in less than a fortnight, has had to be re-sited because of a recurring outbreak of strangles, an extremely contagious equine disease. The event, which starts on September 17, will be held at Loughanmore in Templepatrick, Co Antrim, venue for the junior European championships in 1993.