[swisstrains]

I think that they would be referred to as "traps".
In the event of some over-enthusiastic shunting or if a wagon started to roll away from the sidings this arrangement would prevent them from running out onto the main line. Whenever the points are set for the main line the other points are interlocked so that they always face towards the "trap".
Although a "trap" isn't usually very long I have seen them used to hold a solitary coal wagon to supply a signal box for example. That could possibly have been the case at Redbrook.
If these sections of line were longer and could be used to facilitate shunting between sidings without fouling the main line they would be known as "headshunts" or "necks".