On Tue, 13 Mar 2012 08:52:50 -0000, a l l y wrote:

I've seen this phenomenon often enough to be pretty certain they're a
type of lightning. I now live in rural Cumbria, and was driving home
late last night across a small moorland area when I thought I saw some
wildfire in the distance.

Other (boring) possiblities:

Lamping or even just headlights from distant traffic. Lamping is more
likely to give a "flash" than traffic as the light is swung rapidly.

Flashover on HV power distribution, you do say it's wet.

--
Cheers Dave.
Nr Garrigill, Cumbria. 421m ASL.