Police launched a massive land and air search - but Mrs Webster was inside the public toilets in the town just 200 yards from where CCTV recorded her shopping at 10.30am.
Mrs Webster's son Martin McDonald questioned why no-one checked the toilets were empty before they were locked up and how the police did not look there.
He criticised police for the way they searched the homes of Mrs Webster's relatives in the hours after her disappearance.
Mr McDonald, 46, claims officers appeared preoccupied with the opinion that she was dead rather than alive.
Mrs Webster is now recovering in hospital from her ordeal and her son says her condition is improving following her stroke.
Mr McDonald, from Elgin, Moray, said: "The only consolation is that she doesn't remember the whole thing. It's horrible to think that she was in there all night.
"Obviously, the toilets have just been locked without anybody checking to see if there was anyone inside."
Mrs Webster was seen on CCTV going into the Co-op store around 10.30am on July 31.
She was reported missing by worried husband James, 84, around 5pm after she failed to return to the couple's home in Forres.
Police sniffer dogs were drafted in and helicopters scoured the area as fears grew for her safety.
Mrs Webster was found in the toilet around 8am the next morning - just 200 yards from where she was last seen on CCTV.
Mr McDonald, who works for a car dealership, said: "I wanted the police to help. I wanted my mum found.
"The officers came to Elgin to look in my 80-year-old uncle's house, they looked in my shed, when they could have been looking for her.
"They never said it in so many words, but they were looking for a body."
He revealed officers even scoured the attic of his parents' home - on the apparent theory that Mrs Webster had been dumped there by her husband.
Mr McDonald added: "They looked in the attic at my mum's house. My old man's hardly capable of walking, let along getting in a loft through a 3ft hatch."
A spokesman for Moray Council said: "The council can only apologise most sincerely to Mrs Webster and her family for what must have been a distressing ordeal for all of them.
"An urgent review of procedures will now be done to ensure that where we operate toilets in partnership with the local community who open and close them, as was the case here, there is no prospect of a similar incident happening again."
Chief Inspector Stewart Mackie, Police Scotland's Moray area commander, apologised to Mrs Webster's relatives.
He said: "There have been instances in the past where people have been reported missing when they have taken unwell in sheds.
"We certainly did everything we could in terms of the missing person search and used considerable resources.
"We carried out searches in the area where she was last seen and work under the assumption that when toilets are locked up they are checked, clearly that was not the case this time.
"It's a very tragic set of circumstances."
Source : www.telegraph.co.uk/