Lola and Isabella Koupparis, aged nine months, were found crying and covered in blood after the fox went into their upstairs bedroom and attacked them in their cots in Hackney, east London.

They were taken to the Royal London Hospital in east London after the incident on Saturday night but Isabella was transferred to Great Ormond Street Hospital (GOSH) in central London for further treatment.

A GOSH NHS Trust spokeswoman said: "Great Ormond Street Hospital for Children NHS Trust can confirm that Isabella Koupparis is still a patient at the hospital and continues to receive the highest possible levels of care from medical staff."

The Royal London Hospital said Lola remained in a serious but stable condition.

Meanwhile, Mr Johnson said foxes were a pest and a menace and could in rare circumstances pose a threat to humans, telling reporters: "Therefore it's right that boroughs should focus on their duties for pest control because as romantic and cuddly as a fox is, it is also a pest."

Family members reportedly said that the fox attack could be "life-changing" for the twins.

Their mother, Pauline Koupparis, discovered the tots looking "like something from a horror movie" after the mauling and described it as "like a living nightmare".

Lola had facial injuries and some puncture marks on her arm, while Isabella suffered injuries to her arm and both children underwent surgery, she said.

The fox is thought to have crept in through a door on the ground floor which had been left open because of the hot weather while Mrs Koupparis and her husband Nick watched Britain's Got Talent on television.