Britain believes Crimea is in a different category to the rest of Ukraine and could be afforded special treatment if Vladimir Putin abandons his "KGB mentality", according to Nick Clegg.

In an interview with the Guardian, the deputy prime minister acknowledged that Russia had a "very pronounced imprint" on the peninsula, a sign of how Britain and the rest of the EU acknowledge that Moscow will play a central role in determining the constitutional future of Crimea.

The Liberal Democrat leader called on Putin to embark on a "civilised discussion" with Kiev as he threw his weight behind the interim Ukrainian prime minister, Arseniy Yatsenyuk, who said on Friday that the civilised world would not recognise a referendum on 16 March that is designed to return Crimea to Russia. The Black Sea peninsula has been part of Ukraine since Nikita Khrushchev gave it to Kiev in 1954, then a simple transfer within the Soviet Union.

Clegg argued that pressing ahead with a referendum condemned by Kiev as unconstitutional would simply inflame tensions. This suggests that continuing Russian support for the referendum would trigger the first set of EU sanctions due to be introduced if Moscow declines to open a dialogue with Ukraine.

Clegg was highly critical of Putin's behaviour towards Ukraine, seen in Moscow as central to Russian interests. "I think Putin's reaction is very revealing. It's as if he's been in a sort of deep freeze since the cold war and hasn't moved with the times," Clegg said. "He gives every appearance of applying a KGB mentality rooted in the cold war to new realities in 21st-century Europe. To regard closer ties between Ukraine and a non-military organisation like the European Union as the equivalent to American tanks on your lawn at the height of the cold war suggests to me that we're dealing with a man who's applying yesterday's divisions and arguments to today's problems."

At the same time, Clegg sent conciliatory signals to Moscow when he acknowledged Russia's special links to Crimea, not least the fact that its Black Sea fleet is based in Crimea. He said: "Crimea already has a semi-autonomous status within Ukraine and clearly has a different history to other parts of Ukraine and has a very pronounced Russian imprint on it, not least because of the presence of the Russian Black Sea naval operation. So it is already in a different category and I don't think anyone wants to deny that.

"No one is somehow suggesting that Crimea should be treated exactly the same as other parts of Ukraine given that it hasn't been treated like that in the past by the Ukrainians themselves."

David Cameron is to hold talks with Angela Merkel about Ukraine over dinner in Hanover on Sunday night amid clear signs that Moscow is rebuffing the EU's attempts to encourage a dialogue with Kiev. The prime minister and German chancellor are expected to discuss the Russian attitude towards the planned Crimean referendum and Russia's decision on Friday once again to block observers from the Organisation for Security and Co-operation in Europe from entering Crimea.

Merkel and Cameron may indicate that the EU may embark on the second phase of punishment – travel bans and asset freezes – after the leaders of both houses of the Russian parliament said on Friday they would support a vote by Crimea to join the Russian Federation. Kiev tried to reassert its authority over Crimea, which has been under effective Russian control since the weekend, when the interim Ukrainian president, Oleksandr Turchynov, signed a decree cancelling the planned referendum.

Clegg called on Putin to agree to the EU proposal for a contact group to oversee a dialogue between Kiev and Moscow. "It is now really for Russia to respond. I very much hope they will respond by now agreeing to enter into that contact group and for a civilised discussion to take place between the Ukrainian and Russian governments."

Russia's state-owned energy giant, Gazprom, which claims to be owed $1.8bn by Ukraine, escalated on Friday night tension with an aggressive statement from its chairman about the country's latest missed payment. "We cannot supply gas for free. Either Ukraine clears the debt and pays for current deliveries, or there is a risk to return to the situation in early 2009," said Alexei Miller in Moscow.

The reference to the last time Russia cut off gas supplies to Ukraine was seen as highly significant and sources close to the company admitted the statement was meant to be a "shot across the bows".

Gazprom believes it has the legal right under its supply contract to terminate the deal. British gas suppliers are privately warning that any escalation of the standoff in Crimea that involved the Russians turning off the energy taps to Ukraine could hit UK householders.