I think you may have made a similar mistake to the one I made with numbers. The deaths you quote are England and Wales whilst the population figure (UK) you give includes Scotland and Ireland.    However the ratio idea still works but with different numbers.   Briefly: year        deaths         population           Rate/1000        ASMR                                       (x 1000) 2020       608,002        59,829                  1016.2             1043.5