The move followed news this week NHS England is removing almost 300 patients from St Andrew's mental health hospital in Northampton.

A Charity Commission spokesperson said: ‘We have now opened a regulatory compliance case into St Andrew's Healthcare to assess concerns about the oversight of safeguarding provision by the trustees of the charity, the financial viability of the charity and the wider governance, management and administration of the charity by its trustees. We are engaging with the charity's trustees and other regulators to determine our next steps.'

Chief executive of St Andrew's Healthcare, Dr Vivienne McVey, announced she was standing down following the news of the patient removal.

Unison East Midlands regional organiser Nadeem Samari said: ‘There's understandable anxiety among the workforce about their own futures and the patients they care about so deeply.

‘Hundreds of staff, including nurses, healthcare assistants and support staff, are troubled by these serious allegations. They've had nothing to do with the creation of this crisis.

‘It's disappointing the chief executive chose to retire this week without offering an apology or accepting any responsibility.

‘At a time of such serious failings, there should be a demonstration of openness, regret, and accountability from the leadership. Not stepping aside at this difficult time and failing to address the harm caused.'