An urgent appeal has been issued by the NHS for two regularly required blood types after an increase in demand and the bank holiday weekend has left a significant stock shortage.
Levels of blood types O negative, the "universal" blood group often used in an emergency when a patient's blood type is not known, and B negative, which is required by patients with serious blood disorders like sickle cell, are in short supply.
The bank holiday weekend saw a drop off in the number of donors giving blood, meaning that the stocks of these two groups could fall below two days' worth.
Ideally, around six days' worth of stock of all respective blood groups is needed.
Other long-term factors that have hindered healthy levels of O negative blood include the increasing use of it as an emergency substitute for Ro blood.
This is a rare blood sub-type more common in black people, but many don't know they have it until they donate and there is currently a huge shortage of Ro blood donors.
Levels of B negative, also a blood group more common in black people, are low because many patients with serious blood disorders like sickle cell, a disease which affects red blood cells, need it.
Currently there are 15,000 people living with sickle cell in the UK and over 300 new babies are born each year with the condition.
The NHS Blood and Transplant unit is struggling to match these demands.
There is currently an urgent appeal for more people from the black community to give blood, as NHS Blood and Transplant needs at least 40,000 new black donors to help patients of sickle cell.
Over 7,000 have come forward since the appeal last June, but more are needed to help ease the pressure on blood stocks.
Mike Stredder, director of blood donation at NHS Blood and Transplant, said: "The overall demand for blood is declining year on year. However, the need for specific blood groups such as Ro blood type and O negative are on the increase.
"We need an additional 4,000 regular O negative donors to those we have now to consistently provide seriously ill patients with the blood they need. If you know you are O negative or B negative and have never donated before, now is the time to make a difference.
"If you are O or B negative, please call us on 0300 123 23 23 to get a priority appointment or walk in to one of our fixed site donor centres to give blood."