All UK travel corridors, which allow arrivals from some countries to avoid having to quarantine, have now closed.
Travellers arriving in the UK, whether by boat, train or plane, also have to show proof of a negative Covid-19 test to be allowed entry.
The test must be taken in the 72 hours before travelling and anyone arriving without one faces a fine of up to £500.
All passengers will still be required to quarantine for up to 10 days.
The isolation period can be cut short with a negative test after five days in England, but it does not apply in Scotland, Wales or Northern Ireland.
The government has said the travel corridor closure will be in force until at least 15 February.
Under the new rules, travellers arriving from the Falklands, St Helena and Ascension Islands are exempt.
Those arriving from some Caribbean islands are exempt until 04:00 GMT on Thursday 21 January.
Foreign Secretary Dominic Raab told the BBC’S Andrew Marr Show on Sunday that Public Health England would be stepping up checks on travellers who must self-isolate.
He said enforcement checks at borders would also be “ramped up” and added that asking all arrivals to self-isolate in hotels was a “potential measure” the government was keeping under review.
Passengers arriving into London’s Heathrow airport on Monday said they had been met with “substantial” queues at passport control and one couple complained they had “felt unsafe” due to what they described as poor social distancing.