Thousands of units of donated blood, collected from people in East Anglia, are brought to the NHS Blood and Transplant centre in Colindale.

Up to 200 people work at the centre, testing and creating products from blood before dispatching them to hospitals. Due to the relentless demand for blood, the centre is open 24 hours a day.

The blood is delivered into a reception area and processed in the manufacturing laboratory.

'When the blood is in the reception area, we decide what we are going to do with it,' explained Gus Norville, the acting operations manager at the centre in Colindale. 'If we know the donor, we know what we can use the blood for.'

One donation of blood can be split into three components – red cells, platelets and plasma.

The first stage involves the bag of blood being filtered to capture the white cells before being put in a spinning machine to separate the plasma and red cells. A nutrient called Sag-M is then added to the red cells.

'Cells still respire and produce carbon dioxide so we give them nutrients,' Mr Norville said.

The blood is then tested and when it is bagged and ready to be transfused, it is taken to a large, walk-in fridge where it is stored at 4C.

Blood is collected from donors throughout the day and brought to the centre between 5pm and 3am. 'It takes us a day to get everything done and issue a unit of blood,' Mr Norville said.

To make platelets, the white cells are removed from the blood before plasma is added to the platelets and they are spun down.

'Four separate donations are needed to make one unit of platelets. They must all be from the same blood type.'

Platelets are used to help those suffering from cancer, whose bone marrow is destroyed.

Platelets are live and always have to be kept moving but unlike red cells, which have a shelf life of 35 days, platelets only last a week. Platelets are stored at 25C.

Plasma is frozen and stored at minus 40C and lasts for up to a year. It is used to treat burns victims and help people whose blood can not clot.

'We have to predict how much blood is going to be needed at any one time,' Mr Norville said. 'We have teams which work with hospitals to make sure blood usage is correct and efficient. When we have had major disasters the public has been fantastic and has always come forward. Before the Olympics we had to increase blood stocks. The public support was brilliant.

'We always need to be able to show our trail so the transfused blood can be traced back to the donor.'