Dangerously low blood stocks have sparked an urgent appeal for new donors.
NHS staff absences due to Covid and recent heatwave conditions have resulted in one in five booked appointments being missed.
Hospitals aim to always have six-days of blood supplies but the Mirror understands stocks are now down to 3.7 days.
An amber alert will be triggered if stocks drop to two days supply when planned operations may need to be cancelled.
NHS Blood and Transplant told health chiefs on Wednesday they have enough supplies for a week.
But there are serious concerns that any further disruption, such as more expected heatwave conditions, could push the service over the edge.
Health Secretary Steve Barclay appealed to big-hearted Mirror readers for help when he gave blood in Stratford, East London.
He said: “Although we have enough blood to supply hospitals and services which are running as normal, we urgently need donors to make appointments now to help us re-build stocks.”
NHSBT chief executive Betsy Bassis added: “Please make an appointment to give blood. One pint of your blood could save or improve three lives.”
The Mirror launched a campaign to help NHSBT recruit the 75,000 regular blood donors it is short as the service recovers from the pandemic.
Visitblood.co.uk or call 0300 123 23 23 to register.
