From Boris’ speech tonight.
That is why people will only be allowed to leave their home for the following very limited purposes:
Shopping for basic necessities, as infrequently as possible
One form of exercise a day - for example a run, walk, or cycle - alone or with members of your household;
Any medical need, to provide care or to help a vulnerable person; and
Travelling to and from work, but only where this is absolutely necessary and cannot be done from home.
That's all - these are the only reasons you should leave your home.