Theresa May has been warned that the Government must "get its act together" over its response to the Salisbury attack, as it emerged that a new suite of sanctions against corrupt Russian officials is to be shelved for up to two years.

A so-called "Magnitsky amendment", announced by the Prime Minister as an "immediate action" following the chemical attack in Salisbury, will not be introduced until after the UK has left the EU.

Last night the disclosure prompted a furious response from Conservative MPs who campaigned for the law, which allows the government to target human rights abusers with asset freezes and visa bans.

Ben Wallace, the security minister, has told MPs that the measure, mirroring Magnitsky laws in force in the US and Canada, would not be introduced until "after Brexit". Government officials declined to say whether the comments referred to the UK's formal departure date next March, or the end of the transition period at the end of 2020.

Mr Wallace said the reason for the wait was that it forms part of the Sanctions Act, which constructs an entirely new sanctions regime for the UK for when the country leaves the EU.