LONDON—Regulators have little understanding of risks from banks creating digital marketplaces with tech companies and a framework is needed to spot potential contagion if things go wrong, the European Union’s banking watchdog said on Tuesday. The European Banking Authority’s warning is the latest sign that financial regulators are starting to pay more attention to Big Tech’s increasing links with finance, such as in cloud computing. Finance and tech companies are coming closer together as banks set up digital marketplaces for products like payments and mortgages, as well as other financial and non-financial services, a process which has accelerated since the pandemic began. This means customers can make payments or buy things using their mobile phone which links directly to their bank account. This so-called platformisation helps banks to cut costs and reach a wider range of customers, and includes partnerships with tech groups. Apple Pay, for example, allows banks’ debit …