Quarantine won’t help Boris Johnson, even if it is the right thing to do

It is hard to work out what the prime minister’s calculation is, writes John Rentoul. Perhaps he thinks the level of voluntary compliance is high enough to be effective in controlling the virus

Johnson is faced with the kind of choice that Tony Blair says always faces prime ministers: whether to cut off their arm or their leg (Getty)

Are the quarantine rules just for show? Sometimes Boris Johnson gives the impression that he changes the rules when the scientific advice changes, but without seriously intending to enforce them.

The new rules requiring travellers to isolate themselves for 14 days after returning from Belgium seem to be voluntary. As with the quarantine imposed on arrivals from Spain last month, there seems to be no intention to try to enforce the rules or even to check up on people after they have left the airport.

The same problem besets the track and trace system: there seems to be a large minority of people who won’t be tested, won’t pick up the phone to contact-tracers, and won’t isolate. People don’t want the inconvenience of isolation, and don’t want to be the cause of imposing it on others.