A volunteer doctor who will travel to West Africa to help care for Ebola patients is disinfected during training offered by the German Red Cross (DRK) on October 7, 2014 in Wuerzburg, Germany. Getty Images

Four NHS hospitals have been put on standby to deal with an outbreak of Ebola in the UK.

The warning comes as Prime Minister David Cameron chairs a COBRA meeting to discuss the epidemic ravaging West Africa.

The hospitals on red alert include: The Royal Free Hospital, which treated British nurse William Pooley who contracted the disease in Sierra Leone, Liverpool University NHS Foundation Trust, Newcastle Upon Tyne Hospitals Foundation Trust and the Sheffield Teaching Hospitals Foundations.

However the risk of Ebola to Britain remains low and if a case is identified the UK has "robust" and "well-developed systems" for dealing with "unusual infectious diseases", said Public Health England.

"UK hospitals have a proven record of dealing with imported infectious diseases," said Dr Brian McCloskey, director of global health at Public Health England.

"If an Ebola case is repatriated to, or detected in, the UK they would receive appropriate treatment in an isolation unit, with all appropriate protocols promptly activated. Protective measures would be strictly maintained to minimise risk of transmission to healthcare workers treating the individual."

He added: "It is important to remember that for Ebola to be transmitted from one person to another contact with blood or other body fluids are needed. As such, if England was to see a case of Ebola this will not result in an outbreak here."

The World Health Organisation has not introduced entry screening for the disease in the UK despite calls for it from Home Office minister Norman Baker following the "concerning" development in Madrid.

Spanish nurse Teresa Romero Ramos tested positive for the disease on 7 October after treating two Spanish missionaries who contracted the virus while working in Sierra Leone and Liberia. Her husband Javier and dog Excalibur are both in quarantine. He is urging Spanish authorities not to put down the pet.

The PHE said it has distributed information to primary care and hospital healthcare workers, immigration centres, universities and schools about the outbreak and actions required in the event of a possible case.

"The risk of travellers and people working in affected countries contracting Ebola remains low, but PHE continues to keep border staff and medical practitioners informed, and request they remain vigilant for unexplained illness in those who have visited these areas in West Africa," said Dr Paul Cosford, PHE director of health protection."

Scientists from Lancaster University predicted that there was a 50% chance the disease would arrive in the UK by 24 October.

More than 3,400 people have died in West Africa from the disease. Dallas victim Thomas Eric Duncan remains in a critical condition after travelling back from his native Liberia.

Last night a vigil was held for him by his family, who were joined by nurses and doctors outside the Texas Health Presbyterian Hospital.