Her children knew the housebound pensioner could not be spending it – so they employed DIY detective work, using closed circuit TV cameras to establish the truth.

Camera images showed care worker Michelle Bradshaw, 40, taking the cash –and the evidence was enough to send her to court facing a possible jail term.

Mrs Nadin's children set up the cameras, which look like digital clocks, in two rooms where money was kept and her daughter Janet Womersley, 46, also marked some cash in her mother's purse with her name and address in ultraviolet ink.

When the money disappeared Bradshaw was arrested and was found with the marked notes.

Bradshaw, of Shirecliffe, Sheffield, admitted six counts of theft at Sheffield Magistrates Court, which heard she blamed the credit crunch, her husband and daughter's expensive hobbies, and a holiday for forcing her to steal £160.

Robert Coyne, prosecuting, said Bradshaw had worked for Sheffield Council's dementia team Care4U for three years, looking after Mrs Nadin, 77.

He said the housebound Alzheimer's sufferer, who lived near Bradshaw, had two visits a day from carers.

But in July Mrs Nadin's daughter became concerned that money she had left for her mother from her pension was going missing.

"She knew her mother couldn't have spent it because she is housebound", Mr Coyne said.

The family set up secret cameras in two rooms of Mrs Nadin's house and before long Bradshaw was filmed stealing.

Mr Coyne told the court Bradshaw blamed her crimes on the expense of her husband and daughter's hobbies.

She said that because of the credit she could not afford to finance them, they had a holiday booked and she didn't want to use the money she had saved.

The case was adjourned for pre-sentence reports and Bradshaw was warned she could go to jail.

Afterwards Mrs Womersley said: "You have carers in thinking they're going to look after your mother, and you expect them to look after your mum the way they would want their parents to be looked after. "

Her brother David Nadin, 40, spends three days a week at his mother's house.

He said: "It became obvious that money was going missing.

"Since about June this year we believe more than £1,000 is unaccounted for.

"Once we played the CCTV back with the evidence we went to the police and told them what we had discovered.

"We marked £30, which was in mum's purse, by using ultra violet ink before Michelle Bradshaw came to the house.

"The police arrested her the same day the money went missing and found the marked notes on her.

"This has had an impact on the whole family and it has been very upsetting for mum. She is terrified of anyone who looks like Bradshaw and she has lost all her trust in everybody else."

Eddie Sherwood, Sheffield Council's acting director of adult services, said there would be "a full and speedy investigation".

"This employee was suspended as soon as this matter came to light, he said. "Abuse of vulnerable people is absolutely despicable. We deplore the actions of anyone who betrays their trust and will take appropriate action to deal with them.

"The council works closely with the police and health service to safeguard vulnerable adults and has a dedicated team who will deal, in confidence, with concerns."