How will the 14-day quarantine work and why are Britain’s three biggest airlines are challenging it

The UKs new quarantine rules have come into effect from today. What are the new restrictions on international arrivals and how will they be enforced?
How will arrivals be tracked?
Most people arriving in the UK will need to fill in an online form with contact and travel details and the address where they will be staying in quarantine for the subsequent 14 days. Self-isolating people can shop for essentials such as food and medicine. Random checks will be carried out by Public Health England.
Who is exempt?
A large list of people, including anyone on government or defence business, foreign diplomats, regular international commuters, lorry drivers, medical workers and fruit pickers. By and large, the exemptions are international key workers.
How it will be enforced?
In England, fines start at £100 for not filling in the form, £1,000 for breaching self-isolation and possible deportation for foreign nationals not complying. However, the devolved administrations of Scotland, Wales and Northern Ireland have yet to say whether and how they will enforce the rules for any arrivals in their jurisdictions an anomaly that IAG and others argue undermines the process.
Why do airlines and travel firms object?
Britains three biggest airlines have started legal proceedings against the government in a bid to overturn quarantine rules. Although lockdown rules prevent overnight stays in the UK, and the Foreign Office has warned against all non-essential foreign travel, signs of progress had led airlines to plan more flights over the next two months, after grounding fleets in March. Holiday firms hoped that people would start booking trips. They argue that imposing the rules so late in the pandemic is ineffective, illogical, and will deter visitors and potential outward bookings long after the quarantine rules are lifted.
Why does the government say they are necessary?
The government says the measures are backed by science and will help prevent a second wave of Covid-19 cases imported from abroad, as other countries move out of lockdown, with restrictions on work and movement potentially eased further in the UK in coming weeks.
Have other countries imposed similar quarantine measures?
Yes, many either ensured that arrivals self-isolated or closed their borders to foreign visitors. However, Britain decided against doing so early in the crisis and is now bringing in quarantine just as other EU countries are in the process of opening up.