If you are sefl isolating because you have symptoms . YOU CANNOT GO OUTSIDE. Not for a run ,not to walk the dog, not to get in shopping

[bumblingbovine49]

This is from the government advice page

if you have symptoms of coronavirus infection (COVID-19), however mild, stay at home and do not leave your house for 7 days from when your symptoms started. this action will help protect others in your community whilst you are infectious*

It is very important that you stay at home whilst you have coronavirus (COVID-19). This will help to protect your friends, colleagues and the wider community and will help control the spread of the virus.
www.gov.uk/government/publications/covid-19-stay-at-home-guidance/stay-at-home-guidance-for-people-with-confirmed-or-possible-coronavirus-covid-19-infection

It really could not be more clear DO NOT GO OUTSIDE for 7 days. I would imagine you can go in the garden if you have one , though I personally would wear a mask for the sake of your neighbours since recent research has shown that the virus can stay in the air for around 3 hour..

This is if you have symptoms of a cough or a fever - even if mild

Can you link to the evidence for the virus 'staying in the air'?

They go on to say We realise that staying at home may be difficult or frustrating, but there are things that you can do to help make it easier.. See the link for what those are

It is completely irresponsible for people now not to prepare for the possibility of having to stay at home for 7 days, without needing to go outside, possibly longer if you symptoms worsen. You should only leave the house in emergencies, where it is life or death. That is what you should be doing, no matter how inconvenient it is or how frustrating or how annoying for you personal freedom.

www.telegraph.co.uk/global-health/science-and-disease/coronavirus-could-live-air-hours-surfaces-days-study-suggests/