Question:
How do you set the default CRS in QGIS to be British National Grid?
Answer:
The default Coordinate Reference System (CRS) for QGIS is WGS84 (EPSG: 4326). If you try to create new Vector files, or indeed want to open multiple Raster Images, then working with an incorrect default CRS can slow you down!
In order to change the default CRS for QGIS, choose the Settings > Options menu. Then from the CRS window, change both the Enable Automatic ‘on the fly’ reprojection and CRS for New Layers options to now be British National Grid (EPSG:27700).
Press OK and the change will be applied to your QGIS installation.
So now, the next time that you open multiple Raster Images or wish to create a New Vector File the default CRS will automatically be set to British National Grid!