This evening's briefing was given by the Prime Minister.

More generally in the view of the way people have responded over the last few days to the measures we have set out I want to say a bit more about how we interact outdoors.
Of course I want people to be able to go to the parks and open spaces and to enjoy themselves – it is crucial for health and mental and physical wellbeing.
But please follow the advice and don’t think that fresh air in itself automatically provides some immunity.
You have to stay two metres apart; you have to follow the social distancing advice.
And even if you think you are personally invulnerable, there are plenty of people you can infect and whose lives will then be put at risk.
And I say this now – on Sunday evening – take this advice seriously, follow it, because it is absolutely crucial.
And as I have said throughout this process we will keep the implementation of these measures under constant review and, yes of course, we will bring forward further measures if we think that is necessary.

Robert Jenrick, the Communities Secretary then introduced “Shielding” (Measures to Protect Those at High Risk) in some detail.