Five horses that ran in recent race meetings and under the care of various trainers have tested positive for morphine in their 'A' samples, according to a statement from the British Horseracing Authority (BHA).

Morphine is a prohibited substance on race day but is allowed during training. The test results were reported by LGC analytical laboratory (formerly HFL Sport Science).

The BHA said it will not make public any information regarding the identity of the horses, trainers or owners, the races they competed in, or the dates on which the samples were taken until all necessary processes are completed. The BHA said the process includes counter analysis of respective 'B' samples, if requested by those connected with any of the horses, and its own investigations.

Authorities are investigating whether there could be any link between the cases and, if so, what that link might be. Due to the shared characteristics of these cases, the authority said, it is not possible to rule out further positives from post-race samples obtained in recent weeks. The BHA has been in communication with the National Trainers Federation and trainers of the horses in question on this matter