New rules requiring all people arriving in the UK to self-isolate for 14 days have come into effect.
Those arriving by plane, ferry or train - including UK nationals - would have to provide an address where they would self-isolate and face fines of up to £1000 ($NZ1949) if they did not follow the rules.
Home Secretary Priti Patel said the laws were designed "to prevent a second wave" of coronavirus.
Some industries have warned they would be severely impacted by the rules.
Anyone arriving from the Republic of Ireland, the Channel Islands or the Isle of Man would not have to complete the form or enter quarantine.
There were also exemptions for workers in some industries such as road haulage and medical professionals providing essential care.
All other travellers have to fill in a "public health passenger locator" form on arrival. Failure to do so could lead to a penalty of £100, or travellers may be refused entry.
If they are unable to provide an address, the government would arrange accommodation at the traveller's expense. There would also be checks to see whether the rules were being followed.
The British government has faced criticism from the aviation industry and some Tory MPs over the measures, but Patel said the measures were "proportionate" and being implemented "at the right time".
"The science is clear that if we limit the risk of new cases being brought in from abroad, we can help stop a devastating second wave," Patel said.
Those arriving in England and Northern Ireland could face a fine of £1000 if they fail to self-isolate for the full 14 days, while they face a £480 fine in Scotland. The maximum fine for repeat offenders in Scotland is £5000. The enforcement rules in Wales are not clear.
People should drive their own car to their destination, where possible, and once at their destination they must not use public transport or taxis.
They must not go to work, school, or public areas, or have visitors - except for essential support.
Passengers in transit, who do not pass through border control, are also among the groups who are exempt from the mandatory isolation.
The travel industry has been vocal in its criticism of the government's quarantine rules, warning that the isolation period will deter visitors and put jobs at risk.
The manufacturing industry also highlighted that fewer flights would restrict imports and exports, which would have a knock-on effect for the freight industry and hamper the recovery of some businesses.
British Airways, EasyJet and Ryanair wrote to Procurator General Sir Jonathan Jones, the government's most senior legal official - the first stage required when taking legal action against the government.
The airlines said they were prepared to ask for a judicial review into the government's travel quarantine rules.
Travel trade body Abta called on the government to urgently create a roadmap for restarting international travel, while the UK's biggest airport services company, Swissport, warned it could deliver a "killer blow" to the tourism sector.
'Another blow to our industry'
Industry leaders wrote to Prime Minister Boris Johnson in May asking that the government avoid taking a "blanket approach" to quarantine, suggesting so-called "air bridges" with countries that had low coronavirus rates.
Aviation, maritime and rail industry leaders were invited to discuss the new quarantine plans but British Airways refused to attend the meeting, and aviation bosses told the BBC that they were not impressed by the content of the call.
BBC transport correspondent Tom Burridge said relations between the government and Britain's aviation industry were at "rock bottom".
BA, already under huge financial strain due to the pandemic, proposed making 12,000 staff redundant to stay afloat. Separately, Heathrow Airport's chief executive warned that about 25,000 jobs could be at risk at Heathrow Airport.
Government sources told the BBC the UK was hoping to secure air bridge agreements with certain countries, such as Portugal, Spain and France, as well as Australia and Singapore.
The government's position was that the idea was only "under consideration".
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