Thanks for that link - I've decided to get a couple of pairs of lenses sent from Bike Nashbar (a US supplier) to a relative in Florida, who will post them on to me.
I really like my Bolle shades (they have the only prescription insert that works for me) - I just wish they would leave their successful models unchanged, and make spare lenses available in the UK from sources other than high street opticians, with their silly prices.