Twitter has been fined after failing to file its UK business accounts with Companies House, which were due in September.
Both Twitter and TweetDeck, which it acquired last year, have been struck with automatic penalty charges by the Cardiff-based authority, according to a Sky News investigation. The fines will continue to rise if the companies continue to withhold the accounts.
The returns are used by HM Revenues & Customers as a basis for tax filings, but there has been no suggestion that Twitter has avoided paying the correct amount of corporation tax.
The news comes shortly after a number of tech giants have been criticised by MPs for how they conduct their financials in the UK.
A spokesman for Companies House told Sky: "They are both currently in default on the submission of accounts to us on their respective due dates.
"Companies House records show Twitter's accounts should have been delivered by September 30, but there is no indication this has been done."
He added: "There is no indication at this stage when the accounts will be available but as a matter of routine we will already be in correspondence with the companies to request that they file as soon as possible."
Computerworld UK contacted Twitter for comment on the reports, but had not responded at time of publication.