LONDON — A second police officer has been confirmed as a victim of the nerve-agent attack that nearly killed a Russian former spy and his daughter in England last year, the police said on Thursday, bringing the number of those known to have been sickened in the episode to six.

Forensic testing confirmed that an officer from the Wiltshire Police, who does not wish to be identified, was affected by the nerve agent, Novichok, which was used to target the former spy Sergei V. Skripal, in March 2018. Mr. Skripal’s daughter, Yulia S. Skripal, also fell seriously ill after being exposed to the poison, but both survived.

Tests on a blood sample from a police officer involved in the response to the poisoning, which occurred in Salisbury, England, confirmed exposure to a small amount of Novichok, according to a statement from the Metropolitan Police in London, which coordinates counterterrorism investigations.

The unnamed officer displayed signs of having been exposed to the nerve agent at the time and was given medical treatment, the authorities said, before returning to duties shortly afterward.