Four more cases of equine flu have been found at a Newmarket yard, putting doubt on hopes of horseracing resuming after a six-day shutdown.

The British Horseracing Authority (BHA) said on Sunday night that it had identified the disease in vaccinated thoroughbreds of the Suffolk yard of trainer Simon Crisford.

It added: “No non-urgent journeys should be made to this yard - including by the media.

“At the moment the affected horses are all contained within this yard.

“The Newmarket community - including licensed trainers, veterinary surgeries, farriers, racing school and all other relevant bodies - are being advised to continue to show increased vigilance in biosecurity.”

It said that Mr Crisford, former long-standing racing manager to Godolphin, had been named “in order to ensure the Newmarket community is aware of the yard at which an infection has been identified”.

The news comes after what had appeared to be a positive weekend in the fight against the disease, with no fresh cases being reported either on Saturday or up to a previous BHA statement issued shortly after 4.30pm on Sunday.

Some 720 tests had returned negative on Saturday and around the same total was estimated in addition to that on Sunday, from over 2,000 received by the Animal Health Trust in Newmarket.

Racing in Britain was cancelled on Thursday, following an announcement by the BHA on Wednesday night of outbreaks earlier in the week.