The create_effect() function must be passed a valid Timeline FX as an argument. I am not sure what effect “UK_Legal” is supposed to be, especially since you are trying to load a Batch setup in it.
In the documentation we represent an object between brackets like this but in your script you need to actually pass a real object, not this placeholder.
The easiest way to obtain a PySegment from the Python Console is to use flame.timeline.clip.selected_segments which will return a list of all the segments currently selected in the Timeline. You do not need to do this in a custom actions script since the selection is already passed.
Could you tell us what workflow you are trying to achieve? It would be easier for us to help you.
It is not possible to create a Batch FX or to “manipulate” it using the Python API so the approach you took won’t work.
The only thing similar that could work (but require more steps) would be to create a Timeline GAP BFX clip, keep it in your workspace, create a new track in the desired sequence and overwrite your Timeline GAP BFX clip on that track.