Platforms like Amazon, eBay, Vinted, Etsy and Airbnb are now legally obliged to share how much income sellers make with the UK tax authorities.
As part of the government's effort to clampdown on tax evasion, HM Revenue & Customs (HMRC) has signed up to global rules from the Organisation for Economic Cooperation and Development (OECD) which allow tax officials to share information with their equivalents in other countries.
As well as websites used to sell products such as Amazon and eBay, it also covers platforms and app which allow the provision of taxi and private hire services, food delivery services, freelance work and the letting of short-term accommodation.
Although HMRC was previously able to request information from online marketplaces, the new regulations, introduced on 1 January, mean that all relevant websites operating in the UK must now routinely report information such as sellers' bank account details and the value of transactions.
Official collection of the information began on New Year's Day with the deadline for the first report on 31 January 2025.
An HMRC spokesperson told Sky News:
"Implementing the OECD rules will enable HMRC to exchange information with other tax authorities to access data from platforms based outside the UK quickly and efficiently.