A video has been published depicting a Russian hoax call, with the UK defence secretary Ben Wallace

On Monday, a video of defence secretary Ben Wallace being fooled into chatting on the phone with an impostor posing as Ukraine’s prime minister was released, just hours after Downing Street stated it suspected Russian state actors were behind the hoax.

When the caller asks Wallace questions, he responds with scepticism and apparent perplexity in the short tape.

The UK government had previously warned that the imposters were linked to the Kremlin and could leak a doctored tape of the call with the defence secretary.

“Things must be going so badly for the Kremlin that they are now resorting to pranks and video fakes,” Wallace tweeted. Not the behaviours of a self-assured government, but after the Salisbury Cathedral sightseeing narrative, everything is possible…”

Vovan and Lexus, the prankster duo, claimed credit for the video. They are suspected of having connections to Russia’s security services, which they deny.

The storey raises major concerns about the security and defence deficiencies that allowed pranksters to contact one of the UK’s most senior ministers and persuade him to discuss a highly sensitive military and diplomatic situation in Ukraine.

Wallace appears to be questioned in the video if he will back Ukraine’s nuclear ambitions — Russia has erroneously alleged that Kyiv has nuclear ambitions.

“It’s a doctored clip,” a defence insider stated. What you don’t hear is the defence secretary arguing that the UK cannot be involved in claimed Ukrainian nuclear ambitions since the UK is a signatory to the nuclear non-proliferation treaty.”

The tape was doctored, according to government officials, but the substance of what Wallace appeared to say was not disputed.

Vovan and Lexus, real names Alexei Stolyarov and Vladimir Kuznetsov, are expert prank callers. They previously communicated with Elton John and Turkish President Recep Tayyip Erdoan.

The caller posing as Ukraine’s Prime Minister, Denys Shmyhal, reached Wallace. Priti Patel, the home secretary, and Nadine Dorries, the cultural secretary, were both singled out.

In its first statement blaming Russia for the video calls, No. 10 said on Monday that it believed Russian state actors were to blame.

“The Russian state was responsible for the fake telephone calls made to UK ministers last week,” claimed the prime minister’s official spokesperson.

“This is normal practise for Russian information operations, and disinformation is a tactic straight from the Kremlin playbook to try to divert attention away from their illegal activities in Ukraine and the human rights violations occurring there.”

“We are witnessing a spate of distraction stories and blatant lies from the Kremlin, reflecting [Vladimir] Putin’s desperation as he strives to conceal the scope of the fight and Russia’s failures on the battlefield.”

Wallace confirmed publicly that he had been targeted shortly after his call on Thursday. An investigation into what transpired has been initiated, and a cross-Whitehall assessment is looking into improving security protocols.

There have been numerous such prank calls in the past, but none have been linked to the Russian government.

Boris Johnson, the foreign secretary at the time, spoke about international relations and offensive poetry with a prank caller posing as Armenia’s prime minister in May 2018.

In 2015, it was revealed that an impostor posing as the head of GCHQ, Robert Hannigan, was able to contact the then-prime minister, David Cameron, on his mobile phone.

In another fake, a caller dialled GCHQ and obtained Hannigan’s cell phone number.