You are not going to be rear ended because you slow down for a pedestrian. It's utter nonsense.
And anyway, the damage to your car if someone does go into the back of you is far less than you will do to the pedestrian!!!!!!!!!!!!!!!!!!!!!!!!!
Have I done enough !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
but really, the mind boggles.
The Highway Code applies across the UK, with possibly a couple of differences in NI - this is not one of them - you do not run down pedestrians who are crossing a side road you want to turn into or out of.