re Serengetis in the UK
The 'Driving' section of the Sunday Times has recently been offering a very good deal on Serengeti sunglasses (30% off the RRRP, if I recall correctly. More if you buy more than one pair).
I've had a quick look and, unfortunately, I can't find an online version of the offer.
For the record, go for the 'Drivers' or particularly the 'Drivers Gradient' lenses. I've been using them for the last couple of years and they are very good at improving the contrast, particularly in flat light conditions. Highly recommended.
B73