Kettering South Jn Setback(?) Signals

[richa2002]

I'm curious if anyone knows what purpose these signals served on the up slow at Kettering North Jn before resignalling during electrification works. There were three at regular intervals and plated as 'X1' 'X2' 'X3' from what I can make out.

I've seen suggestions that they were used for freight trains setting back but I'm not entirely sure why they'd be doing this here as there's only a small civil engineers yard to the north of this image. Any info would be much appreciated.