Local residents expressed concerns that the alleged attacker was well known for often erratic behaviour.

Dave Cox, 69, said: “The young man was just walking along the road and saw the incident with Betty so he went over and said, ‘Why did you do that?’ 

“The young boy was just being a Good Samaritan and he’s now dead.”

Mrs Walsh was said to have been a local barmaid whose family is well known in the area. She  is believed to have seven children, 10 grandchildren and 12 great grandchildren.

Gerhard Peleschka , the manager of The Griffin, said Ms Walsh was a former employee at the pub and is a “Brentford legend”.

“This is tragic. Everyone knows her in Brentford. She is always so happy and is as fit as a fiddle,” he said.

“It just blows your mind what happened to her.”

He added the incident was unusual in a close-knit community where “everyone knows everyone”, and described it as “an absolutely safe area”.

Police said there is no evidence linking the stabbings to terrorism and no one else is being sought over the incident.

Additional reporting by Maria Collinge