Light Leaks through Smooth Shaded Object but not Flat Shaded

Any fixes to this? It’s really annoying as I would like to smooth shade this particular object.
I’ve attached two screenshots, first one is flat shaded, second is smooth.

Well, that’s what smooth shading is. You are smoothing the vertex normals over a large low-poly area. What you probably want is to smooth it over a smaller region close to the edges. You could either edit the mesh, add an extra cut there, or create a normal map that controls the normals more precisely.