If you download the complete of each map, it will require approximately the following space:

MapData size in GB

OS Road Map0.3
OS 1:50,000 Landranger3.3
OS 1:50,000 HD Landranger8
OS 1:25,000 Explorer7
OS 1:25,000 HD Explorer27
OS Open Map Local33
OS Vector Map Local Colour    50
GroundRanger    3.3
France 1:1,000,0000.3
France 1:100.0003.5
France 1:25,00028
OS StreetView22