RACING will resume in Britain on Wednesday, following a six-day shutdown because of the outbreak of equine influenza, the British Horseracing Authority has announced.

The ruling body had placed over 170 yards into lockdown in an attempt to halt the spread of the highly-contagious virus, with all meetings last Thursday cancelled the previous night.

However, following a period of extensive testing and after seeking the advice of a series of veterinary experts, the BHA gave the go-ahead for a resumption late on Monday - but with strict biosecurity controls in place.

The BHA's chief regulatory officer, Brant Dunshea, said: "Our approach since hearing about the first positive results last Wednesday has been based on accumulating as much information as we could as quickly as possible so we could properly understand the risks of this virulent strain of flu spreading to more horses.

"That would be harmful to them and damaging to any trainers' yards that became infected.

"It has also been our intention to ensure that we avoid an issue that could result in a long-term disruption to racing with the risk of many of our major events being unduly impacted."

The sport was rocked after it emerged three horses - which subsequently rose to six - were found to have the disease at Donald McCain's stable in Cheshire.

The BHA quickly enforced a cancellation of racing in Britain and confirmed a call would be made on Monday about whether scheduled fixtures at Southwell, Plumpton, Musselburgh and Kempton could take place on Wednesday.

Over the weekend it was announced around 1,500 tests had returned negative - but on Sunday evening it emerged four vaccinated horses from Simon Crisford's Newmarket yard had tested positive.

Dunshea said: "After analysis of thousands of samples, and no further positive tests on Monday, we still only have two confirmed sites of infection. We have put robust containment measures in place around both.

"From the testing and analysis conducted the disease appears to be contained at present. The BHA veterinary committee believe that the swift controls on movement that were put in place have clearly helped to restrict the spread of this virus."

While Dunshea admitted there was a risk associated with a return to racing, he was fulsome in his praise of the work of the Animal Health Trust in Newmarket who carried out the testing.

"There have been significant logistical issues associated with testing and processing so many tests in such a short space of time," he said.

"Fortunately, owing to the tireless efforts of the Animal Health Trust, trainers and their local vets, and BHA staff, the vast majority of yards which had been placed on hold will be in a position to resume racing.

"Clearly, there is some risk associated with returning to racing. This risk has been assessed and, based on the evidence - and ensuring biosecurity measures are in place - the level of risk is viewed as acceptable."

As part of the controlled return, the BHA said it has "developed a risk framework which allows us to categorise individual trainers by the level of risk they have been exposed to.

"The ability of runners to return to racing from those yards will depend on the risk categories the yards are placed in.

"We are finalising overnight which category individual trainers will currently be placed in. The BHA will contact trainers tomorrow morning to inform them of their category and eligibility to run."

Major weekend cards are scheduled for Ascot, where the Betfair Ascot Chase is the feature, Haydock, which will host the William Hill Grand National Trial, and Wincanton, where the Betway Kingwell Hurdle is the headline attraction.

During the blank period some key races in the build up to the Cheltenham Festival should have been run and a handful have now been rescheduled.

Ascot is the main beneficiary and will stage a nine-race card on Saturday, with the addition of the Betfair Hurdle and Denman Chase which should have been at Newbury last weekend.

The Kingmaker Novices' Chase scheduled for Warwick will be at Sandown on Friday, while a Listed Mares' Hurdle from Warwick will be held at Haydock on Saturday and Wincanton's meeting picks up a Listed Mares' Chase from Exeter.

Speaking in a statement earlier in the day, Crisford said: "None of the four horses that have returned positive tests for equine influenza displayed any clinical signs of respiratory illness, including nasal discharge and elevated temperatures, prior to the mandatory swabbing that was undertaken last Friday, February 8.

"The swabbing occurred following Sajanjl's race at Newcastle last Tuesday, February 5, and she has tested negative. There is no obvious connection between Sajanjl and the four identified horses.

"All horses at Kremlin House Stables, totalling 92 boxes, undergo a strict vaccination check and programme on their arrival.

"All four identified horses have been vaccinated within the last six months along with the rest of the yard and in line with vaccination protocol."