A B sample has confirmed the result and Paget's
is set to be taken away at an Equestrian Federation (FEI) tribunal early next year.
Paget said: "I will continue to work... to provide a full explanation."
Former rodeo rider wins Burghley trials
Clifton Promise was tested following his victory at the Burghley International Horse Trials on 8 September.
Equestrian Sports New Zealand (ESNZ) chief executive Jim Ellis told
"What this now means is a rule violation has occurred and Jock [Paget] must now provide a plausible and satisfactory explanation to the FEI over the coming months."
Ellis said he was "confident" Paget would be able to do so but added: "The Burghley title will be lost as a result of this, the rule violation makes that automatic.
"The FEI's tribunal will consider a period of suspension, taking into account the evidence and the facts of the matter. I really can't pre-empt that."
Paget has been suspended from any "official ESNZ activity" while the legal process is under way
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