Are UK financial institutions obliged to use the Open Banking Implementation Entity interface?

There is currently no obligation for UK registered organisations to use the Open Banking Implementation Entity (<a href="/glossarycollection/open-banking-implementation-entity" style="color:#48277C;" target="_blank" title="Open Banking Implementation Entity">OBIE</a>) interface. The use of the OBIE interface is free, and although organisations are required to register with the Financial Conduct Authority (<a href="/glossarycollection/financial-conduct-authority" style="color:#48277C;" target="_blank" title="Financial Conduct Authority">FCA</a>), they are not required to register with the OBIE. 

In general, any interface should be fit for purpose and able to support widespread usage. This means that using the OBIE interface would be sensible for a UK firm but it does not prevent them from using an alternative national or commercial interface.