Thanks All
@macklebee
I didn't realise there were additional plugins for UU3D!
I exported the map as .b3d with the lightmap and imported this into UU3D with the plugin then exported as .fbx into Unity and everything worked out great. All I had to do was change the material shaders to Legacy > Lightmapped so the 3DWS lightmap gets used in Unity.
BTW when I tried doing this with .dbo it didn't import well into UU3D so .b3d is the way to go for Unity.