Woman who was trapped in car for three days dies

Lamara Bell, 25, spent three days waiting for help after being critically injured in a car crash. Photo / Supplied

A British woman who spent three days waiting for help after being critically injured in a car crash that killed her boyfriend has herself died.

Lamara Bell, 25, was found in a car on Wednesday off a motorway near Stirling in Scotland and taken to hospital.

"My sister just passed away," her brother Martin Bell wrote on Facebook on Sunday.

Her boyfriend John Yuill, 28, was killed in the July 5 crash, which was reported to the police but was not followed up for 72 hours.

An investigation is under way.

Police Scotland Chief Constable Stephen House last week apologised to the relatives of the two victims.

"We are all deeply saddened by the news of Lamara Bell's death this morning and I would personally like to express my deepest sympathies to her family and friends for their loss," House said.

"We will continue to cooperate fully with the police investigations and review commissioner as they undertake their investigation into the circumstances of this tragic incident."

-AAP