Top U.K. banks, including Barclays, Lloyds, HSBC, and Natwest, are known as the "Big Four," having long dominated Great Britain's banking sector. However, changes like the rise of fintech (including open banking), Brexit, and COVID-19, have shifted the influence of this "old guard" making it clear that digital banking is essential today. Using Similarweb's Research Intelligence we'll look at the performance of top U.K. banks in 2021 and hone in on one "foreigner" that may be disrupting traditional, home-grown leaders.