A large Russian flag has been draped over scaffolding at Salisbury Cathedral, nearly a year on from the Novichok attack in the city.
The flag appeared over the weekend, with workmen spotted trying to remove it on Sunday morning.
The stunt has been branded "stupid" by Salisbury MP John Glen, and a "slap in the face" by former Salisbury mayor Jo Broom.
The Russian flag visible on Salisbury Cathedral. Image: Chris Maple /PA
Former Russian spy Sergei Skripal and his daughter Yulia were poisoned with the nerve agent Novichok on March 4 last year in Salisbury.
Dawn Sturgess, 44, died after she came into contact with a perfume container used to carry the Novichok on June 30.
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A police inquiry found the two agents from the Russian secret service, the GRU, carried out the attack.
Alexander Petrov and Ruslan Boshirov travelled from Russia to Salisbury, in Wiltshire, via London before spraying the nerve agent on Sergei Skripal's front door.
The Dean of Salisbury, the Very Reverend Nicholas Papadopulos, said: "This was a remarkably stupid thing to do and makes light of the huge personal tragedies involved, and the damage done to the city by the unprecedented nerve agent attacks on Salisbury last year."
A Wiltshire Police spokeswoman said: "We are aware of this matter and inquiries are ongoing. It is not a police matter at the moment."