"Tantalus" uniform and smock, what were they for exactly?

Were these uniforms a trial uniform, or maybe for a specific branch/unit?

As far as I know this stuff consists of these parts but maybe more:
Smock Combat Windproof Mk2 (Modified)
Jacket Lightweight Mk2 (Modified)
Trousers Combat Mk2 (Modified)
SmockWaterproof Mk2 (Modified)
Trousers Waterproof Mk2 (Modified)


I don't have a jacket and couldn't find the pics of my trousers but here is my smock which shows some details that also appear on the other
pieces, mainly mesh bottoms in the pockets.

Tantalus was UKSF issue.

Also had various other items ie Thermals, buffalo smock, Keela produced waterproofs…

Thanks, any idea what specific units used this stuff?
I've seen someone mention something about the SBS, but nothing confirmed anywhere

what goal served all these mesh inserts?

Presumably water drainage, the same as eyelets and grommets typically seen at the bottom of such pockets, only way faster, hence the supposed link to SBS.