The NHS is 'urgently' calling on O Positive and O Negative blood donors to donate following a cyber attack last week in London.

It comes as the NHS reveals this week (National Blood Week) that three blood donations are needed every minute in hospitals to deal with emergencies, childbirth and routine treatments as it calls on more people to become lifesaving donors.

There are around 13,000 appointments available nationally this week in NHS Blood Donor Centres with 3,400 available in London alone.

The NHS is advising all patients to continue coming forward as normal following the cyber-attack.

The IT incident affecting a pathology provider means the affected hospitals cannot currently match patients' blood at the same frequency as usual.

For surgeries and procedures requiring blood to take place, hospitals need to use O type blood as this is safe to use for all patients and blood has a shelf life of 35 days, so stocks need to be continually replenished.

That means more units of these types of blood than usual will be required over the coming weeks to support the wider efforts of frontline staff to keep services running safely for local patients.

O negative is the type that can be given to anyone – known as the universal blood type. It is used in emergencies or when a patient's blood type is unknown. 

Air ambulances and emergency response vehicles carry O negative supplies. Just eight per cent of the population have type O Negative but it makes up for around 15 per cent of hospital orders. 

O positive is the most common blood type - 35 per cent of donors have it – and it can be given to anybody with any positive blood type.

This means three in every four people, or 76 per cent of the population, can benefit from an O positive donation. 

Dr Gail Miflin, Chief Medical Officer, NHS Blood and Transplant said: "Patient safety is our absolute priority. When hospitals do not know a patient's blood type or cannot match their blood, it is safe to use O type blood.

"To support London hospitals to carry out more surgeries and to provide the best care we can for all patients, we need more O Negative and O Positive donors than usual.

"Please book an urgent appointment to give blood at one of our 25 town and city donor centres which currently have good appointment availability.

"We have availability for donors who know they are type O but we also welcome new donors who don't yet know their blood type. You might have one of these special types that can be used in emergencies."

The NHS needs O Positive and O Negative blood donors urgently (credit: NHS).

Professor Stephen Powis, Medical Director for NHS England, said: "NHS staff are continuing to go above and beyond to minimise the significant disruption to patients following the ransomware cyber-attack on Synnovis earlier this week.

"Urgent and emergency services are available as usual so patients should access services in the normal way by dialling 999 in an emergency and otherwise use NHS 111 through the NHS App, online or on the phone.

"But unfortunately, we know that a number of operations and appointments have been postponed or diverted to other neighbouring hospitals not impacted by the cyber-attack, as we prioritise pathology services for the most clinically urgent cases. 

"To help London staff support and treat more patients, they need access to O Negative and O Positive blood, so if one of these is your blood type, please come forward to one of the 13,000 appointments currently available in NHS Blood Donor Centres." 

Paul O'Brien Director of Blood Supply at NHSBT has praised the 'amazing donors' who help save lives everyday through blood donation and urges more donors to come forward this National Blood Week.

He said: "We are hugely grateful for the continued support of our amazing donors who help to save lives everyday by giving blood.

"We simply can't do this without your incredible support and for this we truly thank you."

Following the bank holidays and school half-term holidays, the NHS currently has lower than normal stocks of type O blood and is urging known O group donors to come forward and make an appointment in town and city donor centres across the country.

This National Blood Week also marks the start of a big summer push by NHSBT for new donors to come forward and register.

To book an appointment to donate, visit blood.co.uk, see the GiveBloodApp or call 0300 123 23 23