Horseracing in the UK will resume Wednesday amid enhanced biosecurity measures after being shut-down last Thursday by an equine influenza scare.

The British Horseracing Authority announced late last night that, despite four positive tests being detected on Sunday from horses in the Newmarket stables of Simon Crisford, it is safe to resume. There is an “acceptable risk.”

By the end of last week, six (non-running) horses trained in Cheshire by Donald McCain tested positive to equine flu. Any trainer with runners at the same tracks as any McCain horse in recent days went into lockdown – 174 training yards across the UK went into a round-the clock testing swabbing programme.

BHA chief executive Nick Rust, said: “The decision [to suspend racing] last week was taken with a set of circumstances that suggested to us that we should lock down racing for several days so we could have a clear picture of the circumstances around the outbreak.

“There is an unprecedented level of equine flu at the moment. We were concerned about the threat of this and the impact and disruption it would have on racing in the longer term if we didn’t understand it fully. We are pleased it is contained to two yards and that, under certain controls, we can return to racing.”

There are hopes that one of the major “trial” races for next month’s Cheltenham Festival, the Denman Chase which was part of last Saturday’s Newbury card, may be re-scheduled shortly.

Main concerns centred around the incidence of the Florida clade 1 virus in vaccinated horses. This strain is endemic in north America though not the strain usually encountered in Europe. Clade 1 drastically disrupted Australian racing in 2007, where the Thoroughbred population was not at that time vaccinated.

Many equestrian events and hunt meets voluntarily cancelled over the weekend as a precaution. The British Equestrian Federation advised cancellation was not necessary, but urged vigilance. Amid the non-Thoroughbred population, one case in a vaccinated horse was publicly reported at the weekend.