The company said its cough and cold treatment CCP-08 had received a so-called complete response letter (CRL) from the Food and Drug Administration (FDA), meaning the agency is not prepared to approve it at this time.

Vernalis shares fell as much as 15.8 percent to 16 pence, matching a record low first hit on May 18. The shares, which were trading down 12 percent at 0750 GMT, have fallen 82 percent from their 2015 peak of more than 88.

The FDA blow follows a similar CRL for the company's sister product CCP-07 in April.

"Unfortunately, the outstanding items that resulted in a CRL for CCP-07 could not be addressed in time to avoid the same outcome for CCP-08," Chief Executive Ian Garland said.

Garland said both drugs were "of the utmost importance to Vernalis" and the company was working with its partner Tris and the FDA to resubmit both applications as quickly as possible. It expects to provide an update on progress "in the coming months".

Rx Securities analyst Joseph Hedden said the latest setback was disappointing but not a significant surprise, given the earlier problems with CCP-07.

(Reporting by Ben Hirschler; editing by David Clarke)