A mate of mine (the same one referred to in the Christmas Cracker thread about bats) has been measuring cave waters in the Dales for many years. He reckons that percolation inlets are normally close to 8 degrees C (but points out that the temperature in streamways varies much more, depending on surface temperatures). It's a bit warmer in the south of England; the effect of latitude on cave temperature is apparent even in a small country like the UK. (I remember being amazed the first time I saw folk diving in Wookey Hole (in the south) without any gloves on. I'd never contemplate that in northern England!)