Britain’s prime minister has justified a new raft of quarantines and travel restrictions to some European nations, remarking that in some areas a “second wave” of the pandemic is developing.

The comments come days after the United Kingdom imposed a two-week quarantine for travellers returning from Spain, and as the government added other European nations Belgium and Luxembourg to the restriction list, while also considering adding the Balkan state Croatia as well.

The UK government was extremely slow to introduce any sort of coronavirus-related border control in the first months of the outbreak. Even as almost every other nation on earth imposed restrictions on incomers, the UK’s borders remained totally open, and travellers arriving at airports were not even screened, with approximately 100,000 people flying into the country a week in April.

Border controls were only imposed as the pace of the pandemic slowed worldwide.

Explaining why the government was now acting with haste — whereas before it had taken months to introduce sanitary border controls — Prime Minister Boris Johnson said on Tuesday in comments reported by the BBC: “What we have to do is take swift and decisive action where we think that the risks are starting to bubble up again.

“Let’s be absolutely clear about what’s happening in Europe, amongst some of our European friends, I’m afraid you are starting to see in some places the signs of a second wave of the pandemic.”

The prime minister said the government would continue to add further nations to the quarantine list “throughout the summer” where they deemed it necessary.

Spain is a major tourist destination for British travellers, and the reintroduction of quarantine will be a hard blow to the nation, particularly its rural areas where tourism can be a major economic factor. Spain’s Prime Minister Pedro Sánchez has hit back at the change, saying he was trying to persuade the UK government to roll the move back.

Mr Sánchez said the order was “unjust” and an “error” given how the rising number of cases in Spain was highly localised, with much of the country seeing a low rate of infection presently. The prime minister said coronavirus cases in Spain were actually presently lower than Britain.