The attack on a former Russian spy is being treated as attempted murder

Head of counter-terrorism policing Assistant Commissioner Mark Rowley, right, and England's chief medical officer Dame Sally Davies outside New Scotland Yard, London. Photo / AP

Former Russian intelligence officer Sergei Skripal and his daughter were the target of "attempted murder" using a nerve agent, British police have revealed.

"This is being treated as a major incident involving attempted murder by administration of a nerve agent," Mark Rowley, Britain's top counter-terrorism officer, said.

Skripal, 66, and his daughter Yulia, 33, were found unconscious on a bench outside a shopping centre in the southern city of Salisbury. A police officer who was one of the first to respond to the incident is also in a serious condition in hospital.

Rowley said government scientists had identified the specific nerve agent but he would not say what it was because it was part of the investigation. He also declined to give any details about how it was administered.

What are nerve agents?

VX
A nerve agent with the consistency of engine oil. It was used in the 2017 murder of Kim Jong Nam - the estranged half-brother of the North Korean leader Kim Jong Un.

Ricin
Ricin, the deadliest of the toxins derived from plant material, was used in London in 1978 to murder Georgi Markov, a Bulgarian dissident. He took seven days to die after an assassin fired a poison pellet into him, using an umbrella, outside Aldwych Tube station.

Batrachotoxin
Is an extremely potent cardiotoxic and neurotoxic steroidal alkaloid found in certain species of frogs. Native Indians collect these frogs – Phyllobates terribilis and multicoloured Phyllobates bicolor – and sweat out the poison over a fire before putting it on their darts.

Tetrodotoxin
A neurotoxin often found in puffer fish as well as the blue ringed octopus. Tetrodotoxin poisoning has been described as "rapid and violent", starting with a numbness around the mouth, then paralysis, finally death. The subject remains conscious to the end.

Botulinum toxin
The most poisonous substance known to man. A couple of teaspoons would be enough to kill everyone in the UK, two kilos would kill every human on earth. The same toxin is found in Botox, where a tiny dose is injected to freeze muscles into place, minimising wrinkles.

- additional reporting DPA