The definition of 6 months in the UK entry stamp [duplicate]

Question

I am a Brazilian citizen currently working in a university in the Netherlands. Me and my girlfriend, who is British had a 20 day trip planned back in April. As I came to visit her (for us to go together), our flight was cancelled due to the covid-19 crisis. Moreover, my flight back to the Netherlands was also cancelled, therefore I was not able to leave the UK on the date I planned. I have been doing home office from her house since, now that things seem to be going back to normal, I want to book my flight back to the Netherlands, however, if possible, I would like to avoid for a bit longer to enter in a plane as corona is still a risk.

In the stamp they put on my passport when I arrived it says I can stay for 6 months. I never had to worry about this definition before now, however, how does the 6 months limit work?

1. Are the 6 months renewed every time I come in? Which I find very unlikely, as I mean, seems far too easy to exploit.
2. Are the 6 months renewed on a calendar year basis?
3. Are the 6 months renewed on a 12 month rolling basis?
4. Something else?

I specifically remember that, a couple years ago, a immigration officer at passport control telling me option 2 was the correct. I wanted to confirm this information now, so I called both covid-19 helpline for immigration, and the "general immigration advice" at 0300 123 2241, however, they told me the correct option was 1.

The email I found for immigration queries specific for covid-19 specific did not answer this question, as is not directly related to covid. But I did not manage to find a general email for immigration queries, does anyone know one?

I would be okay with that if I had managed to have it written, but I am worried whether this was just a bad luck of having two officers who did not have the right information. What if later this year I come back to visit her and another officer at passport control also claims option 2 is correct, I would not be able to use the calls as proof that I got the information from an official source.

Should I just assume a worst case scenario and go back as soon as possible?

Answer 1

It's Option 1: the 6 months is renewed every time you enter.

However, as you say that would be very easy to exploit, so it's explicitly not allowed to live in the UK by exiting for a few days every 6 months.

From Gov.uk (this quote is about visitor visas, but as a visa-free non-EEA visitor the same rules apply):

Your visa may be cancelled and you may get a long-term ban on visiting if your travel history shows you’re repeatedly living in the UK for extended periods.

The obvious question then is how much you can get away with, and there's no hard and fast rule, but this answer is about as good as it's possible to get.