【正文】 se output shock, total and corporate writeoff ratios increase. Mortgage arrears, on the other hand, appear to be mainly dependent on household ine gearing. The results suggest that, even if the most extreme economic stress conditions witnessed over the past two decades were repeated, the UK banking sector should remain robust. Key words: Macro stress testing； bank fragility,； loan writeoffs； VAR analysis Summary Stress tests were performed on the resilience of the UK banking system as part of the IMF Financial Sector Assessment Programme (FSAP). These tests revealed that the UK banking system was robust to a number of adverse shocks. Most of these tests were conducted by the large banks themselves,based on scenarios developed from the Bank of England’s Medium Term Macroeconometric pare the robustness of such a conclusion to the choice of stress test, this paper proposes an alternative test of the resilience of the UK banking sector, which analyses the mon developments in a measure of bank fragility and key macroeconomic variables. An advantage of the stress test proposed here is its ability to analyse – within a small system of equations – the increase in bank fragility following a shock to a single macroeconomic variable, allowing for the potential impact on other key macroeconomic variables that may also affect bank fragility. Furthermore, the test allows for feedback effects from an increase in fragility back to the macroeconomy – for example, an increase in the default rate on loans by the household and corporate sectors may cause consumption and investment to fall stress tests used here, like most other methodologies, may not fully capture structural changes in the banking industry. Noheless, the results are robust to a number of checks and uncover some important relationships between macroeconomic dynamics and the loan writeoff ratio – our measure of bank fragility. UK banks’ aggregate writeoffs, and particularly corporate ones, are found to be sensitive to a downturn in economic activity. Household writeoffs, on the other hand, are found to be more sensitive to changes in ine gearing. The results suggest that, even if the most extreme economic stress conditions witnessed over the past two decades were repeated, the UK banking sector should remain approach to stress testing proposed in this paper is straightforward to implement and provides a useful plement to the suite of models used to assess banking sector vulnerability. Introduction Macroeconomic stress tests of the financial system have been developed in recent years (see Se (2021) for a recent survey and discussion). These tests assess the vulnerability of the banking system,or more broadly the financial system, to extreme but plausible adverse macroeconomic tests are important, from a central bank’s perspective, since they are tractable and provide a useful benchmark to assess the risks to the financial system (see Bunn et al (2021)).Recently, as part of the IMF Financial Sector Assessment Programme (FSAP), stress tests were performed on the resilience of the UK banking system. The stress test scenarios were derived from a version of the Bank of England’s structural Medium Term Macroeconometric Model (MTMM). The scenarios were then applied to UK banks’ aggregate loan book (see IMF (2021) and Hoggarth and Whitley (2021)). The main findings of this analysis were that the UK banking system was robust to a range of plausible adverse macroeconomic this paper we adopt a different approach to perform macroeconomic stress tests on the UK banking system and investigate whether the conclusions arising depend on the choice of stress test and on the fragility variable used. We attempt to account for the dynamics between banks’ writeoff to loan ratio and key macroeconomic variables using a parsimonious vector autoregression (VAR) model. Unlike most existing stress testing work on links between the business cycle and the fragility of the banking system, a direct mea