Excel has a limit of ~1M rows per sheet. Total cases in the UK until now are ~500K. So it seems they use 2 rows per case in the sheet. Edit: oops, it seems the

Excel has a limit of ~1M rows per sheet. Total cases in the UK until now are ~500K. So it seems they use 2 rows per case in the sheet. Edit: oops, it seems they used columns for the cases and the ~16K column limit was hit when daily cases exceeded that.