Russia is prepared to launch a series of cyber attacks on Britain and other Nato members as it seeks to weaken support for Ukraine, a senior Cabinet minister will warn in a major speech next week.

Moscow will “not think twice” about exploiting defence gaps to target UK businesses, and allies must “not underestimate” the threat it poses, Chancellor of the Duchy of Lancaster Pat McFadden will say.

Mr McFadden will also warn that cyber interference enables Russia to “turn the lights off for millions of people” and represents the “hidden war” it is waging against Kyiv, as first reported by the Sunday Telegraph.

In a speech to the Nato Cyber Defence Conference at Lancaster House, the minister is expected to say: “Military hard-power is one thing. But cyber war can be destabilising and debilitating. With a cyber attack, Russia can turn the lights off for millions of people. It can shut down the power grids. This is the hidden war Russia is waging with Ukraine.”

He will add: “Given the scale of that hostility, my message to members today is clear: no one should underestimate the Russian cyber threat to Nato. The threat is real. Russia is exceptionally aggressive and reckless in the cyber realm.”

Mr McFadden is expected to specifically call out Unit 29155, a Russian military unit that the Government says was previously found to have carried out a number of attacks in the UK and Europe.

There are gangs of “unofficial hacktivists” and mercenaries not directly under the Kremlin’s control “but who are allowed to act with impunity so long as they’re not working against Putin’s interests”, he will say.

It comes after South Korea, a Nato Indo-Pacific partner, was targeted in response to its monitoring of the deployment of North Korean troops to Kursk, where Russia is fighting against Ukraine.

The attack has been widely attributed to a pro-Kremlin cyber gang, with Mr McFadden warning that such groups act with “disregard” for geopolitics and “with just one miscalculation could wreak havoc on our networks”.

“Russia won’t think twice about targeting British businesses in pursuit of its malign goals. It is happy to exploit any gap in our cyber or physical defences,” he will add.

“It means making sure that businesses and other civilian organisations are doing everything they can to lock their own digital doors. Their security is our security.”

The Cabinet Office minister is expected to set out details of how the UK will seek to boost its protections against emerging cyber threats in a speech on Monday, as well as how the country is stepping up work with Nato allies.

He and senior national security officials will also meet business leaders next week to discuss how they can protect themselves.