Firstly I am in Ireland, but google makes me think it is the same in the UK.
Around where I live there are plenty of very busy, narrow, country roads that are 80km (50mph). Filled with many cars, tractors, lorries etc.
Some people walk these roads or run on them. I know legally they are allowed to but I think it is pure madness. There is one person who is often out walking with a baby in a pram. I have had to stop and wait to pass as there is a stream of traffic coming the other way. But I have also nearly been hit by a lorry who coming around a bend met her and over took as he would never have stopped in time.
I don't go around corners at 80km but I proceed as 'expecting something to be there' but it's still a shock to find a lorry on your side!
There is also a person who regularly runs towards the traffic (as recommended) in roughly the middle of the lane and does not move closer to the side.
I pass other people who are aware of the traffic around themselves and adjust. When my car was broken I walked into town a few times and would step in when a car came.
AIBU to think that while yes you are legally allowed to do this, no it is not a good idea?