I use Nikwax products for all my waterproofing needs and let me assure you that it won't let you down. I use their leather proofing for my mountaineering boots which I've walked for hundreds of miles in under all sorts of crazy Scottish and Icelandic weather conditions. The stuff is magic.

I use the spray version to waterproof my Barbour wax jacket and the laundry stuff to proof cheap water 'repellant' jackets I've bought at service stations on the M6. Excellent stuff.