Aren't people in carehomes being certified as dying of COVID at all? Is it assuming every care home death is COVID and saying they haven't been counted?
Yes they are but they aren't included in the figure being announced daily by the government. You have to get that data from the ONS figures which are published weekly but deaths can not show on there for weeks due to the way the system of registering deaths work. Normally its not an issue as people are only looking at the data for longer term trends, not looking for daily updates.
There's two issues. The figure the government are updating daily isn't accurate, it is only hospital deaths. All evidence points to the true figure being far higher.
Then you have the issue with consistency of data between countries. Thats why when you want to compare countries you're best off looking at the difference between the expected number of deaths for this time of year and the actual number of deaths. Doesn't matter what country your in, if you're dead that's it and you count as 1 person on the figures.