By Saturday April 4, the check-up quickly established that Mr Johnson’s condition had worsened. Mr Reynolds ‘cleared the PM’s diary completely’, but by the following afternoon it was clear there was no choice but to take him to hospital.

A source said Mr Johnson was conscious when he arrived, but ‘very, very unwell’.

He was put on oxygen via a tube through his nose within ten minutes of arrival.

Concerned by the possible public reaction to the PM’s incapacitation, Downing Street described his admission as a ‘precautionary step’ for tests, adding that Mr Johnson would be receiving a ministerial red box so he could continue to work from his hospital bed.

In reality, his condition worsened throughout Sunday evening and Monday.