HOME Secretary Amber Rudd has called for “cool heads” as anti-terror officers investigate the attempted murder of former Russian spy Sergei Skripal and his daughter Yulia.

But the government was under pressure to explain how attacks like this could happen to British citizens.

It came as investigators say a sarin gas-like nerve agent was used to deliberately poison the father and daughter.

Speaking after a meeting of Cobra, the UK Government’s emergency council, Rudd said the process of working out what happened, and when it happened would be a “lengthy and ongoing process.”

The minister said: “We need to keep a cool head and make sure that we collect all the evidence we can, and we need to make sure that we respond, not to rumour, but to all the evidence that they collect, and then we need to decide what action to take.”

Asked how concerned the public should be about their own safety, Rudd said: “We’ve taken all the action necessary to ensure that the public are safe and I’d like to reassure the public that we have the ability and the wherewithal and the knowledge to keep them completely safe.”

She added: “I want to make sure that this investigation responds to evidence, not to rumour, but I can reassure the public and your viewers that all action is going to be taken to keep everybody safe.”

The SNP’s Martin Docherty-Hughes, who serves on the Commons defence committee, said the government had questions to answer, but he also had little doubt about who was behind the attack.

“I speak to the Embassies of our Baltic friends on a regular basis, and while it is obviously too soon to establish the origin of this attack, there is no doubt that it fits a pattern of previous state-sponsored attacks on those connected with Russian business or government all over Europe.

“In addition, the UK Government has real questions to answer about how this has been allowed to happen: a decade after the death of Alexander Litvinenko and attacks like this – regardless of whether they are state or non-state - are still happening, and that is deeply worrying.”

During Prime Minister’s Questions, Theresa May said she was considering whether ministers and dignitaries should attend the World Cup in Russia if Moscow is found to behind the poison scare.

May, answering a question in parliament yesterday, said: “Depending on what comes out in relation to the investigation, into the attack on the two individuals that took place in Salisbury, that it might be appropriate for the Government to look at whether ministers and other dignitaries should attend the World Cup in Russia.”

Investigators yesterday confirmed that medical and chemical evidence pointed to a nerve agent.

Met assistant commissioner Mark Rowley said: “We continue to carry out extensive inquiries. This investigation is at the early stages”.