The British nurse fighting for her life in the Royal Free Hospital after contracting Ebola remains in a critical condition but she has “stabilised”, the Health Secretary said today.

Jeremy Hunt gave an update on Pauline Cafferkey’s condition as charity Save the Children launched an investigation into how she was infected - but conceded it may never establish the exact circumstances.

Mr Hunt told the Commons he had spoken to the doctor leading Pauline Cafferkey’s care at the Royal Free Hospital in north London.

He said: “As has been reported, Pauline’s condition has deteriorated to a critical state although she stabilised yesterday and continues to receive the best possible care.”

Mr Hunt went on: “She said in Sierra Leone that she hoped her loved ones would be proud of her. Well, she should know today the whole country is proud of her for her bravery and dedication to the service of others.

“She stands, quite simply, for the very best of NHS values.”

Mrs Cafferkey, a Scottish public health nurse, was transferred to a specialist unit at the Royal Free in Pond Street, Hampstead, after being confirmed as having contracted Ebola.

She had volunteered with Save the Children at the Ebola Treatment Centre in Kerry Town, Sierra Leone, before returning to the UK. The charity said today that it was urgently reviewing its protocols.

Charity spokesman Rob MacGillivray said they had launched an “extraordinary review” to ensure that they “leave no stone unturned to, as far as possible, identify the source of this infection”.

In a statement released later, Save the Children said its “serious event review” is investigating how Mrs Cafferkey contracted the disease by reviewing training, safety protocols, how protective equipment is used and “working practices”.

The charity stressed that it may not be possible to be “100% sure” how the infection happened.

It said in a statement: “The early findings of the review will be made available by Save the Children as soon as possible.

“As with other Ebola infections in health facilities, it may never be possible to be 100% sure how the patient was infected.

“The work of these brave health workers is never risk-free, but we are committed to doing everything possible to learn what happened and, if necessary, to make changes to our protocols and practice.

“Staff safety is our number one priority and our thoughts are with Pauline and her family at this very difficult time.”

Mrs Cafferkey’s diagnosis has brought fresh scrutiny on the UK’s preparations for Ebola cases.

Mr Hunt said the risk to the public remains low but stressed vigilance was required, reiterating the chief medical officer’s prediction that the UK can expect to see a “handful” of Ebola cases.

He told MPs: “Both the chief medical officer and the NHS England medical director, Professor Sir Bruce Keogh, are satisfied that at this stage we have made sufficient preparations.

“However, they stress that although the risk to the public remains low, we must remain vigilant and be constantly prepared to adjust and improve our processes and protocols as this rapidly changing situation evolves.”

Outlining a timeline of the handling of Ms Cafferkey’s care, Mr Hunt said her temperature was tested seven times before she flew from Heathrow to Glasgow and she was cleared to travel.

She later became feverish and followed advice given to her at Heathrow to contact local services and was admitted to an isolation facility at the Brownlee unit in Gartnavel Hospital, Glasgow, at 8am on December 29.

After a blood sample tested positive for Ebola, she was transferred in a military plane to the Royal Free Hospital by 8am on December 30.