The Royal Mail’s postcode to NGR and Lat/Long database has been leaked and is available from http://wikileaks.org/wiki/UK_government_database_of_all_1%2C841%2C177_post_codes_together_with_precise_geographic_coordinates_and_other_information%2C_8_Jul_2009
The information is now public and whilst the Royal Mail are not happy there is little they can do about people using the information.
The file is about 21Mb and is compressed with bzip2. People with computers running proper software will be able to uncompress that with no problem whilst Windows users will need to download a bzip2 compatible uncompressor. Uncompressed it is about 240MB and is a simple comma delimited text file. Excel can happily read it. There is no address information included, it is merely postcodes to NGR and latitude and longitude.
The availablity of this data should finally end any questions about which postcode applies to any particular UK SOTA summit.