the costs of their tickets are, well ....high
And to put it into context, in 2012 the passenger revenue (fare and ancillary) of BE UK was £565.6m and they carried ~7.6m passengers. As such, their average one-way fare (based on passengers and not seats), including ancillaries, was £74.42. (Excluding ancillaries, it was £60.70.) Given their strategic position and their broadly targeted customers, this average fare doesn't strike me as being particularly high. Of course, it looks worse given their their average sector length is short (466km, 290mi), hence their high yields.