We can use OGR2OGR a command line opensource programme, that converts between a wide range of different formats.
Download info is available here. FWTools is available on Windows, Mac, Linux.
OGR can also reproject the data.
ogr2ogr -f “KML” -s_srs “EPSG:27700” -t_srs EPSG:4326 OutputFile.kml InputFile.shp
will take the UK OS and make it work on Google Maps (e.g. above) or Google Earth.