A modular construction system includes an elongate construction element (1) comprising an elongate body (2) including a longitudinal web (3). The web defines opposite first and second edges (4,5) and a longitudinal centreline (6). The first and second edges are spaced from the longitudinal centreline by a pre-determined distance. A longitudinal first flange (7) of uniform width extends transverse to the web along the first edge in a first plane, and defines a flange edge (9) at a pre-set separation from the web. The elongate body defines opposite first (10) and second ends, and the elongate body has, at the first end, a first end plate (11) orthogonal to the longitudinal centreline. The first end plate defines a first aperture (12) at a selected distance from the first plane. The first aperture is provided in the plane of the web.