The three-week lockdown of the UK began with immediate effect at 8.30pm on Monday evening.

Boris Johnson summed up the new restrictions with a three-word command: Stay at home.

However, the prime minister also outlined a number of exceptions. So how exactly will the lockdown work?

When can I leave my home?

There are only four reasons you should leave home, according to the government.

1) Shopping: Buying basic necessities, for example food and medicine, but as infrequently as possible. (This does not include panic-buying crates of toilet roll).

2) Exercise: “One form of exercise a day, for example a run, walk, or cycle – alone or with members of your household.

3) Medical care: “Any medical need, or to provide care or to help a vulnerable person.”

4) Work: “Travelling to and from work, but only where this absolutely cannot be done from home.”

What shops are still open?

Many high street shops and department stores have already closed but the new restrictions apply to all “non-essential shops and public spaces”.

That includes all retail stores selling clothing and electronics, hair salons, markets, libraries and youth centres, indoor and outdoor leisure facilities such as bowling alleys, hotels and B&Bs, campsites, caravan parks.

Parks will remain open but the communal places within them, such as playgrounds, sports courts and outdoor gyms will be closed.

Churches will be closed except for funerals attended by immediate families.

What about taking my children to school?

If you work in a critical sector (also described as a ‘key worker’), or your child has been identified as vulnerable, you can continue to take your children to school.

Do I work in a critical sector?

The government has issued separate guidance on key workers whose children can continue to go to school. It is a long list so you may well be on it.

In short, the critical sectors are defined broadly as health and social care, education and childcare, transport, food, public safety and national security, utilities (oil, gas, electricity), financial services (e.g. banks), communication, and public services such as the justice system, charities, frontline staff, and some journalists, as well as local and national government.

Can I go to the pub?

No. All pubs, restaurants, cinemas and theatres closed last week, remember?

Can I go out to meet my friends?

No. Boris Johnson said explicitly: ​”You should not be meeting friends. If your friends ask you to meet, you should say no.”

The government has also confirmed it will “stop all gatherings of more than two people”.

However there are two exceptions: gatherings of people who live together, such as parents going out with their children, and gatherings that are “essential for work purposes”.

Social events such as weddings and baptisms will also cease.

Boris Johnson bans gatherings of more than two people

How will this be enforced?

The prime minister said police and other authorities would have the power to issue fines to anybody caught flouting the lockdown.

Officers will also be able to disperse gatherings if people do not comply with the restrictions.