Helen Holland, 81, from Birchanger, Essex - named by the BBC - was left in a critical condition after the collision at around 3.21pm on Wednesday in west London.

Her family said on Friday that she is in a coma.

Her son and daughter-in-law Martin and Lisa-Marie Holland told the broadcaster they were "shocked and sickened at her extensive injuries".

"She is being well cared for by the NHS who we must thank deeply for their help in keeping her alive," they said.

The family is reportedly calling for a "thorough investigation".

Ms Holland had been in London visiting her older sister when the incident occurred at the junction of Cromwell Road and Warwick Road.

On Thursday, Buckingham Palace released a statement on behalf of Sophie, who is the wife of the King's brother Prince Edward, the Duke of Edinburgh.

It said the duchess's "heartfelt thoughts and prayers" were with Ms Holland and her family.

"She is grateful for the swift response by the emergency services and will keep abreast of developments," the statement read.

"Further comment at this time would not be appropriate while the incident is being investigated."

Eyewitness, Fiona El-Lasbi told Sky News that the victim was "hit at speed".

"Let's just pray that she makes it," she added.