Shapefiles from Nationalgrid without a .prj file - what projection are they in?

Question

Im working with these shapefiles:

http://www2.nationalgrid.com/uk/services/land-and-development/planning-authority/shape-files/

They show pipelines & electricity grid of the UK. They do not have a .prj file included in the shapefile.

They display fine in QGIS when layered on top of each other, but I need to know which projection they are in so I can display them on a world map.

The x and y values are very large so I tried the Universal transverse Mercator projection "WGS84/UTM zone 30N ESPG:32630" because the UK is in zone 30.
This placed the shapefiles at the right scale, but just above the equator by Ghana (48 degrees too far south and 3 degrees too far west).

This seems to imply that the shapefiles' coordinates are zeroed half way between UTM zone 30U and 31U.
http://en.wikipedia.org/wiki/File:Utm-zones.jpg

Does anyone know which projection I should be using?

Thanks for your help.

Answer 1

The files are in EPSG:27700 OSGB 1936 British National Grid.

Make sure you have the 7 parameters +towgs84 installed. There are 3-paramater datasets around, which have some offset.