Moscow claimed Gavin Williamson has "lost his grasp on reason" as the Defence Secretary stepped up his warnings about Russian aggression.
Mr Williamson said Russia could cause "thousands and thousands and thousands" of deaths in an attack on Britain's infrastructure and has announced a new radar station to monitor the "severe and real" threat from Moscow.
The Defence Secretary said Russia had been looking at the UK's critical infrastructure such as power stations and interconnectors that allow the transfer of electricity across borders.
But the Russian defence ministry dismissed the claims - and suggested Mr Williamson had "lost his grasp on reason".
Ministry spokesman Major General Igor Konashenkov said Mr Williamson's comments were like something from Monty Python.
"Gavin Williamson in his fiery crusade for military budget money appears to have lost his grasp on reason," Russian news agency Tass reported Maj Gen Konashenkov as saying.
"His fears about Russia getting pictures of power plants and studying the routes of British pipelines are worthy of a comic plot or a Monty Python's Flying Circus sketch."
In a sign of the UK's unease about President Vladimir Putin's military activity, the Ministry of Defence announced a new £10 million radar facility to monitor Russian planes.
The facility on Unst in the Shetland Islands will improve the RAF and Nato's monitoring of the airspace north of Britain and further out across the Norwegian Sea.
Mr Williamson said: "We will always protect our skies from Russian aggression.
"This radar is a vital part of the UK's defences as we react to intensifying global threats and reinforce our ability to tackle them.
"Russia's actions are not limited to Europe's eastern borders - the threat to British livelihoods is severe and real."
The station, which will be ready to operate soon, returns the island to the role it played during the Cold War when it hosted an early warning radar.
It will provide information to the quick reaction alert operation, which sees aircraft launched to police UK and international airspace - jets have been scrambled 69 times in the last five years.
The announcement about the Saxa Vord facility comes after Mr Williamson told The Daily Telegraph that Russia was looking at electrical infrastructure "because they are saying, 'these are the ways we can hurt Britain'".
Mr Williamson speculated the threat could be carried out in the form of a cyber attack, from undersea activity or a missile.
He said: "The plan for the Russians won't be for landing craft to appear in the South Bay in Scarborough, and off Brighton Beach.
"They are going to be thinking, 'How can we just cause so much pain to Britain?'
"'Damage its economy, rip its infrastructure apart, actually cause thousands and thousands and thousands of deaths, but actually have an element of creating total chaos within the country'."