Then, on top of that, according to British investigators, the two men discarded a vial that carried the Novichok so carelessly that a British woman died after her boyfriend found it months later and, thinking it was perfume, brought the bottle home as a gift.

In the RT interview, Mr. Petrov and Mr. Boshirov insisted that they had such a keen interest in medieval ecclesiastical architecture and burning desire to see Salisbury’s cathedral that they traveled to Britain for a weekend getaway that included two separate trips to Salisbury and two nights in a grungy London hotel. They firmly denied any connection to Russian military intelligence, now called the G.U. but until recently known as the G.R.U.

Their account — which included claims of knee-deep slush and “transport collapse” that forced them to abandon a first visit to Salisbury on March 3 and try again on March 4, the day of the nerve agent attack — struck many Britons as so risible that a columnist in The Guardian suggested that “comedy is now diplomacy by other means.”

There was some snow in Salisbury at the time but none of the weather-induced “havoc” cited by Mr. Petrov and nothing that might normally deter two fit Russian men accustomed to harsh winters from walking a few hundred yards from the railway station to the cathedral. And why, if they were so keen to see the cathedral, did they head in the opposition direction from the station and wander into Mr. Skripal’s neighborhood on the other side of town?

“The whole situation is some kind of extraordinary coincidence — that’s all,” Mr. Petrov told RT, “What are we guilty of?”

Their story certainly did not win over many people in Britain and elsewhere, or help burnish Russia’s image.

The interview also left many Russians, even some sympathetic to the Kremlin, shaking their heads. It was so bizarre that a television critic, Arina Borodina, claimed that Ms. Simonyan, the RT editor, had not really met the two men and that footage of her asking them questions had been spliced together with their answers, delivered in a secret location under supervision.