All distances are as the crow flies. It will obviously be further to actually travel to a club.
Distances will be approximate as they are calculated from the centre of your postcode district, which have an average diameter of around 6km. In built up areas such as London postcode districts are not very large (down to 0.29km across), and hence distances will be reasonably accurate. However, in rural areas postcode districts may cover a large distance (up to 66km across), so distances will not be so accurate, but will still give you a good indication of how far away each club is.
There is no free and legal way of translating postcodes to latitude/longitude (unlike in the US). So we have used a free subset which only contains postcode districts. If anyone knows any different please contact the webmaster.