A list of more than 1,000 addresses of New Years Honours recipients, including those of senior police officers and politicians, has been accidentally published by the UK government.
The file was uploaded to the official website, but has since been removed.
The Cabinet Office told the BBC: "We apologise to all those affected and are looking into how this happened."
Among the addresses are those of Sir Elton John and former director of public prosecutions Alison Saunders.
Also on the list of 1,097 honours recipients are high-profile names like cricketer Ben Stokes, former Conservative Party leader Iain Duncan Smith, TV cook Nadiya Hussain, and former Ofcom boss Sharon White.
A government spokesman said: "A version of the New Year Honours 2020 list was published in error which contained recipients' addresses," he said.
"The information was removed as soon as possible.
"We have reported the matter to the ICO [Information Commissioner's Office] and are contacting all those affected directly."
The ICO, which has the power to fine organisations for data breaches, said it will be "making enquiries".
Simon Winch, a sustainability professional from London, was among those who were able to access the sensitive information.
He told the BBC: "I clicked on the link on the gov.uk website at around 11pm on Friday and the spreadsheet opened up.
"At first I thought everyone on the list had given their permission to publish their personal addresses. But then I saw that some quite sensitive names were on there."
Another source told the BBC they accessed the file just after midnight on Saturday but were unable to do so by 05:00 GMT.
The Cabinet Office said the document was visible for around an hour.
Most of the entries in the spreadsheet include full addresses - including house numbers and postcodes.
The addresses of six people honoured for their services to defence are not listed but other potentially sensitive addresses - such as those of some police officers - are.
A separate list, that does not appear to be involved in the breach, covers gallantry awards for police, ambulance and fire staff and military personnel.