Thanks – the reason I worry is because of wordings like this:

As an EU national, you can go to the UK for a period up to three months without any conditions or formalities up until 31 December 2020.

Looking further into it, I found that you need to be a 'qualified person' to stay longer than three months. The way to prove that you are a QP is by getting a registration certificate, but according to pages like this one,

You do not need to apply for a registration certificate.

So I guess this condition does not need to be formalised unless it's called into question?