Traces of the Novichok nerve agent have been found in the blood of a second police officer following the chemical attack in Salisbury last year.
The officer was part of the response team for the March 2018 poisoning which left former Russian spy Sergei Skripal and his daughter Yulia fighting for their lives.
The Metropolitan Police said the officer - who does not wish to be named - displayed signs which indicated exposure to a small amount of the deadly nerve agent and was treated accordingly by medical professionals.
He returned to his duties shortly afterwards.
While the unnamed officer recovered quickly, those who suffered from high levels of the nerve agent became critically ill, or passed away.
Along with the Skripals, Detective Sergeant Nick Bailey also became seriously ill after being exposed to the chemical.
Months later, Dawn Sturgess and her partner Charlie Rowley became seriously ill in Amesbury, where there were admitted to hospital.
Ms Sturgess passed away, however Mr Rowley managed to survive.
It was determined Mr Rowley unknowingly gifted Mr Sturgess the bottle of perfume believed to have been used in the attack on the Skripals and then discarded.
The public have been reassured that there there is a low risk to public health at this point, however the investigation is still ongoing.
Met Police have said the incident has been "unprecedented in its complexity and scale and has involved thousands of exhibits."
“Officers continue to work closely with scientists and experts to meticulously and methodically review and examine the evidence available to us.”
They are also continuing to seek information about the activities of the two wanted men known as Alexander Petrov and Ruslan Boshirov, who are accused of carrying out the attack while they were in the UK between March 2 and 4 2018.