Prefabricated former for constructing underground chamber

A prefabricated former for an underground pumping station comprising:

• a floor former;
• a plurality of vertical support elements, wherein each vertical support element is joined to the floor former around a periphery of the floor former;
• a side wall secured to and surrounding the plurality of vertical support elements, the side wall having an inner layer and an outer layer defining a cavity therebetween, the inner layer and outer layer extending below the floor former, wherein the inner layer extends less far than the outer layer towards a bottom end of the side wall, and
• an opening at an upper end of the side wall in communication with the cavity for receiving concrete,
• the side wall extending both above and below the floor former for defining a space above the floor former and a space below the floor former, and
• an opening being provided between the cavity and the space below the floor former enabling concrete to flow through the cavity and into the space below the floor former;
• when set, the concrete forming a unitary wall and base.