Lightning caused by cosmic rays?

On May 8th, BBC2 television's 'Nature's Wildest Events' had a piece on lightning – with the admission scientists did not know what actually caused it to happen. This was a bit of a surprise as the BBC is inclined to endorse and recite the consensus view, on almost anything. At http://phys.org/print287054805.html … we learn that a paper in the journal Physical Review Letters, by two Russian physicists, A Gurevich and A Karashtin, claim to have found evidence to support the idea lightning is caused by cosmic rays. The proposal was first made in 1992 – but was not of course taken up in the West. However, as no one knows what actually causes lightning to form and strike the hypothesis is as equally valid as any other idea. The oft quoted view is that lightning originates as a result of collisions between ice crystals in cloud etc. Gurevich is convinced lightning is formed as cosmic rays come into contact with water droplets in clouds, causing the air to ionise, resulting in free electrons. These, boosted by the electric field already present in the cloud, become high energy particles that eventually give way to a discharge (the visual aspect of lightning) (see also http://prl.aps.org/abstract/PRL/v110/i18/e185005)