A charity supporting transgender children and young people has issued an apology after thousands of emails were made public online.
Mermaids UK said it was "deeply sorry" for what it called a "historical data breach" after it was first reported by the Sunday Times.
The paper claims the correspondence included "intimate details", names and addresses, but the charity denies this.
Mermaids said it had taken immediate action and reported the breach.
In an official statement on the Mermaids UK website, the charity claimed that the emails were from 2016 and 2017, and that they were searchable only "if certain precise search-terms were used".
It maintained there was "no evidence" the information had been retrieved by anyone other than the Sunday Times, or those contacted by their journalist.
A Mermaids spokesperson told the BBC the emails were shared to a private group on a private messaging platform.
They insisted that the 1,100 emails were between executives and trustees of the charity, discussing matters relating to their work.
"To be clear this is absolutely not Mermaids service users emailing each other, and their emails and private correspondence being available to an outside audience," the spokesperson said.
The Times, however, reported that the emails contained "intimate details of the vulnerable youngsters it seeks to help".
It said the emails could be found simply by typing in the charity name and its charity number.
Mermaids UK stated it had notified the Information Commissioner's Office, the data protection watchdog, and contacted those affected.
The Charity Commission had also been notified, it said, and an independent investigation into the breach would be launched.
"We're going to be employing a third party to oversee processes and advise on how we can improve internal practice," the spokesperson told the BBC.
"I think it's important to note that this dates back some two years when Mermaids was a smaller charity dealing with the first aggressive onslaught from those who are opposed to giving vulnerable transgender children and young people the safe spaces they need."
Mermaids UK was formed in 1995, and is the country's leading charity in services offering support around gender and identity to children and young people up to 20 years old.
It recently received £500,000 from the National Lottery Community Fund.