This is a screen-capture (12 July 2017) of the web-page

http://www.well.ox.ac.uk/~gav/bgen_format/bgen_format_v1.2.html

which documents the BGEN file formats used in some of the UK Biobank genetic data.

Please refer to, and reference in any publications, the original web-page rather than this frozen document.

This resource can be downloaded or viewed using the link: bgen12formats.pdf

If you have wget available (typically on linux systems), then you can also obtain a copy using the command

 wget  -nd  biobank.ctsu.ox.ac.uk/ukb/ukb/docs/bgen12formats.pdf