As European states prepare to make major decisions that will affect relations with Russia, EU members that have maintained cordial ties with Moscow despite the Ukraine crisis appear to be going cold on the Kremlin.

Moscow will closely watch Britain’s June 23rd referendum on EU membership, and a June 28th-29th summit of the bloc’s leaders in Brussels. They will be followed by a July 8th-9th gathering of Nato leaders in Poland, where the alliance is expected to boost troop numbers near Russia’s western border.

Britain’s vote will either reaffirm or deeply shake European unity, with implications for co-operation with the US and within Nato; the EU summit will see discussion of whether to extend economic sanctions on Russia, and how the bloc should manage ties with Moscow amid warnings of a new cold war.

These debates come at a time of troubles for the EU, as fallout from a sharp economic downturn and a continuing migration and refugee crisis fuel the growth of populist parties, which denounce the political elite and European integration.

The EU can only extend sanctions by unanimous approval, and it needs cohesion to maintain pressure on Moscow to end its support for the separatist uprising in Ukraine – so anything that splits the bloc is helpful for Russia.

In the short-term, that rift could come through Brexit; in the mid-and long-term, it could be caused by prolonged turbulence over migration, and the rise to power of Eurosceptic groups from either end of the political spectrum.

“The only country, if the truth is told, that would like us to leave the EU is Russia,” said British foreign secretary Philip Hammond.

“That should probably tell us all that we need to know.”

Britain’s relations with Moscow have been glacial since 2006, when Russian security service whistleblower Alexander Litvinenko was murdered with radioactive polonium in London, with the suspected approval of the Kremlin.

But now other countries, with far warmer ties to Moscow, are trumpeting the danger posed to the EU by Russian president Vladimir Putin.

“This discontent with the EU in Britain . . .is a big chance for Russia to be more powerful in Europe,” Czech foreign minister Lubomir Zaoralek warned this week.

“If the institutions are weak, then Putin will be able to take advantage of them.”

The Kremlin has declined to comment on the British referendum, but Russia’s state-controlled media, including the RT (Russia Today) television station, give extensive coverage to fierce Eurosceptics like UKIP leader Nigel Farage.

Moscow is accused of backing anti-EU parties with hard cash as well as airtime, and France’s National Front has admitted receiving a €9 million loan from a Russian bank.

Mr Zaoralek told the “Financial Times” that Mr Putin was “using our weakness” and that his apparent backing for radical parties was “regularly discussed.”

“We have no doubt Russia is finding ways to finance this,” he added.

“This right-wing populism is very dangerous because it could really destroy the European mainstream. The long-term Russian strategy is divide and conquer.”

The comments were striking given the Czech government’s moderate line in relations with Russia and the fact that the country’s president, Milos Zeman, has held several cordial meetings with Mr Putin and has always criticised the sanctions.

Bulgaria has also sought to balance ties between Brussels and Moscow, but its president, Rosen Plevneliev, this week added to criticism of Mr Putin.

“The Kremlin is opposing us and trying to destabilise the EU,” he said.

“It is trying to destroy and bring down the foundations of the European Union which are unity, solidarity and rule of law.”

He also urged the EU never to accept Russia’s 2014 annexation of Crimea, saying: “If the West allows this, it will be a historic shame. For me, for us, Crimea is Ukraine and Ukraine is Europe.”

Whether national politicians are motivated more by fear for the EU’s future, or for what the rise of Eurosceptic radicals might mean for their own political futures, is unclear.

But EU diplomats are now quietly briefing that sanctions against Russia will almost certainly be extended beyond July — until at least December — despite complaints from countries including Hungary, Italy, Greece and Cyprus.