Where is the source for this, how is the 'average' calculated? Which ages does it include?
Here's some of the findings of the 2023 Survey of Adult Skills (OECD)
Countries outperforming England in literacy:
Finland (296), Japan (289), Sweden (284), Norway (281), Netherlands (279), Estonia (276), Flemish Region (Belgium) (275)
Countries not significantly different from England in literacy:
Denmark (273), Canada (271)
Countries significantly lower than England in literacy:
Switzerland (266), Germany (266), Ireland (263), Czechia (260), OECD average (260), New Zealand (260), United States (258), France (255), Singapore (255), Austria (254), Croatia (254), Slovak Republic (254), Korea (249), Hungary (248), Latvia (248), Spain (247), Italy (245), Israel (244), Lithuania (238), Poland c (236), Portugal (235), Chile (218)
https://www.gov.uk/government/publications/survey-of-adult-skills-2023-national-report-for-england