As seen in March, the ‘stay at home’ rule will be legally enforceable during the six-week national lockdown, the Prime Minister announced in a televised address this evening (Monday, January 4 2021) and police will be able to issue fines to people who flout coronavirus measures.
But as well as being able to leave home for things like exercise and shopping for groceries, there are a whole host of other "reasonable excuses", which are as follows:
WORK- although you must only leave home for work purposes where it is unreasonable for you to do your job from home
ESSENTIAL’ SHOPPING- you can leave home to buy essential items such as groceries or to obtain services. You can also leave your home to do these things on behalf of a disabled or vulnerable person or someone self-isolating
EDUCATION AND CHILDCARE- you can only leave home for education, registered childcare, and supervised activities for children where they are eligible to attend. Access to education and children’s activities for school-aged pupils is restricted. See the gov.uk website for more details on this.
VOLUNTEERING- you are permitted to leave home to carry out volunteering or charitable services
MEETING OTHERS AND CARE- you can leave home to visit people in your support bubble, to provide informal childcare for children under 14 as part of a childcare bubble, to provide care for disabled or vulnerable people, to provide emergency assistance, to attend a support group (of up to 15 people), or for respite care where that care is being provided to a vulnerable person or a person with a disability, or is a short break in respect of a looked-after child.
EXERCISE- you can continue to exercise alone, with one other person or with your household or support bubble. This should be limited to once per day, and you should not travel outside your local area
MEDICAL REASONS- you can leave home for a medical reason, including to get a COVID-19 test, for medical appointments and emergencies
HARM AND COMPASSIONATE VISITS- you can leave home to be with someone who is giving birth, to avoid injury or illness or to escape risk of harm (such as domestic abuse). You can also leave home to visit someone who is dying or someone in a care home, hospice, or hospital, or to accompany them to a medical appointment
ANIMAL WELFARE REASONS- such as to attend veterinary services for advice or treatment
COMMUNAL WORSHIP AND LIFE EVENTS- you can leave home to attend or visit a place of worship for communal worship, a funeral or event related to a death, a burial ground or a remembrance garden, or to attend a wedding ceremony. You should follow the guidance on the safe use of places of worship and must not mingle with anyone outside of your household or support bubble when attending a place of worship.Weddings, funerals and religious, belief-based or commemorative events linked to someone’s death are all subject to limits on the numbers that can attend, and weddings and civil ceremonies may only take place in exceptional circumstances
There are further reasonable excuses. See the gov.uk website.