The UK currently has 1,657,270 positive cases of COVID-19

[Ms. Toad]

17. A representative sample must still proportionately mirror the population.

Testing is not a random process - it is heavly biased toward people who have some reason to believe they have COVID.

For example - if you went to the southern US states and surveyed 7 million people as to whether they spoke Spanish - would you really expect to be able to just multiply that ratio by the population of the US and accurately predict how many Spanish speakers there are in the entire country?

That's one of the reasons that using land lines for political surveys is generally not considered valid. The population which still relies on land lines is not represesntative of the population as a whole. It skews older, and likely more conservative.

To extend from a representative sample ot the general population, the sample has to be truly representative - it is not just quantity that matters. The distribution must match the population as a whole as to the relevant variable.

Good statisticians can adjust for some of that - but to do so you need to know what the mix is, and how it compares to the population as a whole. You have made no attempt to do that - and I would be incredibly surprised if that data is even compiled anyplace publically available.