Nigeria has become the latest country to be added to Britain's travel red list - which imposes stringent coronavirus testing and quarantine restrictions on people who wish to enter.
They will have to pay for and self-isolate in a pre-booked government-approved hotel for 10 days.
Ten southern African countries have already been added to the travel red list, because of fears about the Omicron coronavirus variant.
The government says the decision is temporary and will be reviewed in three weeks.
The travel industry has described the changes as a "hammer blow".
There's concern that Omicron could spread quickly and even replace the Delta variant around the world.