Returning to UK with a disease.

Galloping Truthitis would prevent them entering the UK, as politicians would be terrified of contracting it.

Any sign or otherwise of a sniffle and you go into quarantine, but you can float over on a dingy with drug-resistant TB and no-one gives a stuff. The NHS has a magic money tree remember.

Rabies or ebola would be candidates, anthrax or cholera is another.

Specialist medical evacuation might be needed in such cases.

There is a fairly long list of UK notifiable diseases that you would be very unlikely to be allowed to travel with (as in not allowed to leave the host country rather than not being admitted to the UK):

If you are a British citizen, it doesn't stop you entering the country.

However, if you have Covid, Ebola, or a host of other diseases, you are likely to find it very hard to find someone to transport you. It's this that 'disbars' you.

Would Covid have that effect?

Would a UK-resident British citizen with a recent positive test be refused entry to the UK?

I can quite see that it might result in a refusal of entry to other countries (Austria springs to mind).

Well apparently you might have been brainwashed into being a terrorist of course, if that counts. I think there are notifiable diseases, but you would need to ask the foreign office. Also of course carriers that bring you in ask this sort of question in certain parts of the world. I don't think Yellow fever is encouraged. Brian