Russian cyber gang Qilin has claimed responsibility for the attack on 3 June which has caused significant disruption at St Thomas' and King's College Hospitals and some GP services. The group claimed to have published 400GB of the confidential information on the internet on 21 June.

Synnovis said it was ‘too soon to be able to confirm the exact nature' of the stolen data but confirmed there was no evidence of patient test requests and results being posted.

The pathology services provider said some administrative working drive information containing patient identifiable data had been published.

A spokesperson said: ‘We and the technical experts who are supporting us are working as fast as we can to try to be able to confirm more details and appreciate that waiting will potentially cause people some concern. We will keep our service users, employees and partners updated as the investigation progresses.'

An NHS England spokesperson said: ‘Local health systems will continue to work together to manage the impact on patients with additional resources put in to ensure urgent blood samples can still be processed, while laboratories are now able to see historic patient records.'

National Crime Agency director Paul Foster: ‘The National Crime Agency is leading a criminal investigation into the recent cyber incident affecting hospitals.

‘We are aware data has been published and we are working closely with the National Cyber Security Centre, NHS England and our international law enforcement partners, to progress our investigation and support the incident response.

‘As the investigation is ongoing. I'm unable to comment further at this time.'