An old horse trough in Hoxton has been given Grade II listed status after one man spent two years investigating the origins a cryptic dedication carved into the stone.

Thousands of people each month will walk past the old Metropolitan Drinking Fountain and Cattle Trough Association fountain, now a flower bed, and take no notice of the message.

But Peter Hindley, who lives in nearby Buttesland Street and has a keen interest in local history, would regularly walk past and wonder why it was so vague - "In memory of a beloved friend" is all it says.

"It's been in the area 110 years," said Peter. "But unlike all the other troughs that say: 'In memory of the local vicar or doctor', it doesn't have a name.

"I've walked past it so many times and thought it was fascinating but done nowt about it. One day I thought I would see if I could find out what it is all about."

Peter first went to the Drinking Fountain Association, as it is now named, and looked through records to find it was paid for by a woman named Edith Melvill in 1910.

In the same file, the same question he was asking was written down: "Who is beloved friend?".

"I thought: 'That's fascinating, I've got to investigate it'," said Peter.

He remembered reading something about the East India Company and an officer named Melvill on the website of the London Metropolitan University and went back to research more, eventually discovering who Edith was.

"She was one of six children born to captain Henry Melvill, who was an officer in the Bengal Cavalry. I read the family history but I kept thinking: 'How does this link with the fountain association?'."

Peter then discovered the origins of each trough had been split up among the archives, but through dogged research he tracked down the letters Edith Melvill had sent to captain Simpson from the association, which were as "clear as the day she wrote them" - unlike the poor quality carbon copies of captain Simpson's typed correspondence.

They revealed the fountain, funded through donations, was initially meant to be put in Harlow, Essex, and then Friern Barnet but problems with the local authorities led it to what was then Shoreditch.

More significantly the letters revealed the reason the dedication was to an unnamed "beloved friend".

"You'd never guess it in a million years," said Peter. "What happened was her mother and her had lost their favourite dog named Jill and they wanted a memorial. They wanted the dedication to be to their beloved dog Jill but captain Simpson recommended they didn't do that.

"At the time the anti-vivisectionists were very active. They had put up a statue in Battersea Park in memory of the dogs.

"On the other side were a huge number of people who appreciated what vivisection was doing for medicine and progress. There were lot of medical students who were enraged.

"The statue in the park had to be protected, there were three policemen on 24-hour guard - all at the cost of the local authority.

"It finally came to a head with the Brown Dog Riots in Trafalgar Square. The authority in Battersea decided it couldn't afford to guard this statue and took it down in the dead of night and melted it down.

"Because of all of this captain Simpson suggested to Edith they shouldn't use the word dog. He said it would be at risk of being defaced or give rise to riots and local upset.

"And so that's why it was simply: 'In memory of a beloved friend'.

"In 110 years nobody had been interested enough to find out that reason but after I had done so I wrote it up and made an application to Historic England saying it really deserved to be Grade II listed. And it was granted!"

Historic England said the trough, one of seven left of the original 15 in Hackney, was under threat by definition as it was not listed, and made the designation on grounds of architectural and historic interest.

"It's a fascinating story," Peter said. "I managed to solve a mystery dating back to 1910!"