The government must do more to protect key infrastructure against "hybrid attacks" from Russia, a former national security adviser has told the BBC.
Lord Ricketts said more money should be spent on the defence budget, as well as improving the resilience of energy, transport and air traffic control.
He warned hybrid attacks were becoming "more reckless, more dangerous" and that people could end up being killed.
It comes after MI5 chief Sir Kevin McCallum said in his annual speech earlier this week that threats from foreign states, including Russia and Iran, had quadrupled in the last decade.
Lord Ricketts told BBC Radio 4's Today programme that ministers had to warn British people about what might be coming.
"Not only is [Russian President Vladimir] Putin trying to break morale in Ukraine, he's also trying to undermine morale in European countries," he said.
He said there had been a stark warning from the head of MI5 that there could be worse to come in terms of hybrid attacks in the UK or on other Nato territory.
Responding to a question about the impact of disruption by Russia, Lord Ricketts said: "I'm not saying there's going to be industrial war with tanks rolling across the north German plain.
"But yes these hybrid attacks are getting more reckless, more dangerous...people are going to end up getting killed somewhere."
Hybrid attacks tend to use non-military methods, such as hacking, in an attempt to destabilise a country.
Moscow is suspected to be behind many such attacks in Europe since the start of the war in Ukraine, but it has always denied involvement.
As well as cyber-attacks, hybrid attacks can include attempts at sabotage and efforts to spread misinformation.
Lord Ricketts's warning comes after US President Donald Trump blocked sanctions on Russia. Ukraine's President Volodymyr Zelensky said the decision "only encourages him [Putin] to keep attacking" Ukraine.
The former national security adviser, who also previously ran the Foreign Office, said the UK's focus should be on putting more effort into the coalition of the willing, rather than attempting to act as a bridge between Zelensky and Trump.
"I don't think in Trump's current mood there is any influence Britain can have in the short term," he said.
A growing number of European leaders have warned that Russia may be preparing attacks to test their commitment to supporting Ukraine.
Last month, Germany said Russia was responsible for a drone attack on an airport in Leipzig, in which an explosive failed to detonate close to Ukrainian cargo planes.
French President Emmanuel Macron warned in September that the threat of hybrid attacks by Russia against Europe and France had intensified.