The UK National Security and Investment Act 2021 (the “Act”) entered into force on January 4, 2022 and enables the UK government to screen, block and unwind certain transactions on national security grounds. A new body, the Investment Security Unit (“ISU”), is responsible for the operation of the new regime. The Act provides for mandatory prior notification and approval of certain transactions in 17 sensitive sectors, and for the retrospective “call-in” of other transactions. The new regime does not only apply to M&A. The new powers could also potentially apply to lending (especially secured financings) and restructuring and, until the ambit of the legislation becomes clearer, a cautious approach is advised. Lenders are well advised to consider whether the Act would apply to their lending and restructuring transactions, and the implications for the deal timetable and execution risk. Mayer Brown partners David Harrison and Trevor Borthwick give an overview of the new powers and discuss the key factors to consider at each stage of a lending transaction: signing/closing, trigger events during the tenor of the facility and enforcement/restructuring.