Matt Hancock is considering legal action against Isabel Oakeshott, the co-author of his Covid diaries after she leaked a huge cache of his private messages.

The former health secretary was at the centre of a growing political storm following the unprecedented leak of 100,000 WhatsApp messages, which is likely to see the release of private discussions involving dozens of ministers and officials.

Mr Hancock came under immediate fire from bereaved families after messages were released suggesting he had rejected official advice to test all residents going into care homes – a claim he hotly disputes.

The messages were leaked by journalist Isabel Oakeshott, who was a ghostwriter on Mr Hancock’s pandemic ‘diaries’.

Friends of Mr Hancock last night said he could take legal action to prevent the further disclosure of messages he considers to have been ‘stolen’.

A spokesman for Mr Hancock said he was ‘considering all options’, adding: ‘She’s broken a legal non-disclosure agreement. Her behaviour is outrageous.’

Downing Street suggested the Information Commissioner’s Office could investigate whether the leak breached data protection laws.

Mr Hancock was also facing questions about why he entrusted the sensitive material to Ms Oakeshott, who was a well-known opponent of the Covid lockdowns.

The data watchdog last night said the leak raised fresh questions about ministers’ use of WhatsApp but said it was not launching an investigation into the data breach ‘at this stage’, citing journalistic exemptions in the public interest.

Ms Oakeshott defended her decision to publish the emails, saying the public deserved to know the truth now, rather than wait for a public inquiry which could take years and might result in a ‘whitewash’.

But former health minister Lord Bethell, an ally of Mr Hancock, accused her of betrayal, adding that the public deserved the full truth from the public inquiry, rather than a version based on ‘a few scrappy WhatsApps’.

‘It is outrageous that this distorted account of the pandemic is being pushed with partial leaks, spun to fit an anti-lockdown agenda, which would have cost hundreds of thousands of lives if followed. What the messages do show is a lot of people working hard to save lives,’ a spokesman for Hancock said.

Rishi Sunak said the public inquiry into Covid was the ‘right way’ to establish the truth about the handling of the pandemic.

The Daily Telegraph Wednesday indicated it would publish exchanges between Mr Hancock and Mr Sunak, who was Chancellor during the pandemic.

The Prime Minister is understood to have reviewed his exchanges with Mr Hancock yesterday to establish what might be revealed.

Downing Street confirmed that Mr Sunak does discuss government policy via WhatsApp.

But a source said he was ‘very cautious’ about the messages he sends.

Jean Adamson, whose father died in a care home in April 2020, told Good Morning Britain she felt ‘sickened’ by the revelations.