The daughter of a former Russian double agent who was poisoned alongside her father in a nerve agent attack in England is now stable in hospital, doctors have said.

Yulia Skripal was “improving rapidly” after being exposed to Novichok on March 4th in Salisbury, Wiltshire. Her father, ex-spy Sergei Skripal, remains in a critical but stable condition in hospital.

Police believe Mr Skripal and his daughter, who was visiting him from Russia, first came into contact with the deadly chemical at his home in Salisbury.

Dr Christine Blanshard, medical director for Salisbury District Hospital, said: “I’m pleased to be able to report an improvement in the condition of Yulia Skripal. She has responded well to treatment but continues to receive expert clinical care 24 hours a day.”

Detailed forensic testing revealed the highest concentration of Novichok was found on Mr Skripal’s front door. The Metropolitan Police said traces of the nerve agent had been found at some of the other scenes detectives have been working at, but at lower concentrations.

Detectives will now focus their inquiries in and around the address, and specialist teams will step back from some of the other areas investigated over the past few weeks.

Britain has accused Russia of being behind the poisoning – allegations fiercely denied by Moscow. In turn, Russia has suggested that UK intelligence officers may have been involved in the poisoning.

The Kremlin allegation came as Moscow faced increasing global isolation, with at least 26 countries expelling a total of more than 130 diplomats, many suspected spies.

Britain insists there is no plausible alternative explanation for the attack, and has dismissed the series of suggestions emanating from Moscow as nonsense.

About 250 counter-terrorism detectives continue to work around the clock on the investigation, which is expected to continue for months. – PA