The advice given recently was that although the risk of just passing someone closely is minimal it is best practice to keep the 2 metre distance where possible. There is some evidence that viral load may play a part in how badly a person reacts to the virus so again it would seem sensible to reduce exposure to as low as possible.
Anyway I would rather be overcautious, it's better that way.
I just follow the NHS instruction which is what you say:
Important
These reasons are exceptions – even when doing these activities, you should be minimising time spent outside of the home and ensuring you are 2 metres apart from anyone outside of your household.
https://www.nhs.uk/conditions/coronavirus-covid-19/