NHS Test and Trace contacted Cabinet Office Minister Michael Gove when he returned from Portugal.
But why isn't he self-isolating?
What is Test and Trace?
It's a system for identifying people who have been in close contact with someone who has Covid.
Even if they have no symptoms, those people are asked to self-isolate for 10 days - so that, if they do have the virus, they won't pass it on.
Each UK nation has its own contact-tracing service:
Why isn't Michael Gove isolating?
The Cabinet Office minister watched the Champions League final in Portugal on 29 May.
When he got home, NHS Test and Trace told him he had been in contact with someone who had tested positive for Covid.
Most people in that position would have to isolate for 10 days, but Mr Gove is taking part in a trial which makes him exempt.
The trial, launched in May, offers up to 40,000 people in England who have been traced the option to take seven daily tests instead of isolating, as long as their results continue to be negative.
Mr Gove was contacted through the NHS Covid-19 app. But when the trial was announced, the government said it wouldn't include "people identified as a contact through the NHS Covid-19 app or through an informal channel".
A spokesperson for the minister said he had "followed Covid-19 regulations and guidance at all times and will continue to do so".
How does Test and Trace work?
People who have tested positive for coronavirus are contacted by app, text, email or phone.
They are asked to go to a website and give personal information, including:
- name, date of birth, postcode
- who they live with
- recently-visited places
- details of people they have recently been in close contact with
Close contacts must have taken place within a nine-day period, starting 48 hours before symptoms:
- people you've spent at least 15 minutes with, at a distance of less than 2m (6ft)
- sexual partners, people you live with or have had face-to-face conversations with, at a distance of less than 1m
What happens if I am contacted?
If you are approached because one of your contacts has tested positive, you must stay home for 10 days from your last point of contact with them.
You must self-isolate, even if you don't have symptoms.
Others in your household don't have to self-isolate unless they develop symptoms. But they must take extra care around you regarding social distancing and hand washing.
Refusing to self-isolate is illegal in England, with fines ranging from £1,000 for a first offence, to £10,000 for more serious breaches.
What about sick pay?
Employers must ensure that people self-isolating who can can't work from home receive sick pay.
What about the contact-tracing app?
There is an NHS Covid app for people in England in Wales, which you can download on a smartphone.
If two phones running the app are close for a long enough time, and one of the two owners later shares a positive coronavirus test via the app, then the other will receive an alert.
According to research published in May, the app has prevented thousands of deaths.
Why has Test and Trace been criticised?
A committee of MPs published a report in March that said test-and-trace had made no "measurable difference", despite costing £37bn over two years.
Transport Secretary Grant Shapps said: "If we didn't have the test-and-trace system, we would have been in a much, much worse position."
A report seen by the BBC in May claimed failures in England's test-and-trace system were partly responsible for a surge in the Indian variant in Lancashire. For three weeks in April and May, eight local authorities did not have access to full data in their areas.
The Department for Health and Social Care said a "software issue" had led to "a delay in tracing contacts of a number of cases".