British efforts to secure fresh European Union sanctions on Russia after the dramatic unmasking of the prime suspects for the Skripal poisoning could be thwarted by EU countries soft on Vladimir Putin, diplomats have warned.

Theresa May and Jeremy Hunt, her foreign secretary, have signalled they want tougher, new EU sanctions on Russia after the investigation linking the Russian government directly to the nerve agent attack and further US measures on Russia but EU sanctions need the unanimous support of all 28 member states.

“We will also push for new EU sanctions regimes against those responsible for cyber-attacks and gross human rights violations and for new listings under the existing regime against Russia,” the prime minister said in her address to the House of Commons on Wednesday, which exposed how Russian military intelligence carried out the attack.

As an EU member state, Britain cannot impose its own unilateral sanctions on Moscow, although it can and has taken other action. Ben Wallace, the security minister, said on Thursday that would change after Brexit and Britain could go it alone.

British sources confirmed that, although no formal request had yet been made, they planned to drive for new EU sanctions against Russia and to implement new tough counter-measures to deter future attacks.

Diplomats are keen to leverage the last eight months of Britain’s membership of the EU but are still “taking the temperature” of their European allies.

Their hopes will have been bolstered by a statement of support from France and Germany on Thursday, which said the countries had "full confidence" that Russia was behind the attack.

But EU diplomats told The Telegraph that Britain would not be guaranteed to get the necessary unanimous support for new sanctions because countries such as Austria, Greece, Cyprus and Hungary could block them.

“I am not sure Mrs May would be supported if she asked for new sanctions,” a diplomat based in Brussels said, “there is something to the argument that they would be blocked. It only takes one country to say ‘no’ and Italy, for example, has gone softer on Russia.”

Italy’s new government has also called for better relations with Mr Putin, while Germany, while supportive publicly, has embarked on a controversial gas pipeline project with state-owned energy giant Gazprom.

The diplomat, from a country friendly towards Britain, added, “The EU has shown solidarity with Britain based on the assumption that Russia was responsible for the chemical weapons attack. This new evidence proves that assumption right. Does that justify further sanctions? I am not sure it does.”