The British Horseracing Authority has announced four cases of equine influenza have been identified in vaccinated thoroughbreds at the Newmarket yard of trainer Simon Crisford.

A statement from the BHA read: "The horseracing community in Newmarket is tonight being informed that four positive tests for equine influenza have been returned this evening in vaccinated thoroughbreds at the yard of a licensed flat trainer in Newmarket.

"The affected yard is that of Simon Crisford, who has been named in order to ensure that the Newmarket community is aware of the yard at which an infection has been identified. No non-urgent journeys should be made to this yard – including by the media – and anyone who wishes to travel to the yard is advised to first contact the trainer’s office.

"This yard is one of the 174 which has been required to undergo testing due to the fact that runners from the stable competed at the fixture at Newcastle on 5 February, which had been identified as a potential risk fixture. At the moment the affected horses are all contained within this yard.

The sport's organisers had hoped racing would recommence on Wednesday, however, this latest development is likely to delay any return.

The statement went on to say: "A further update will be issued as early as possible tomorrow. This will include further details of action that is being taken off the back of this incident, and how the process will operate for the decision which will be made tomorrow evening regarding whether it is possible to resume racing on Wednesday 13 February."