Swimming

MG - my 2 cents woth (based on just swimming from a young age but not having any kind of formal coaching in recent years)...
Front crawl and backstrokes kicks are different motions. When you're doing front crawl you do little controlled butterfly kicks from the hips keeping your legs pretty straight and your toes pointed - force is downwards.
When you do backstroke, you're bending your knees a bit more and the force comes from the upwards motion, not the downwards motion. I feel my kicks are bigger and more powerful when I do backstroke than crawl. For crawl I think the kick is more for stabilising the body.
Some things I've found are useful:
Bilateral breathing..... seems to be the key to long distance swimming (for me). Only really stuck with it this summer, and now I always breath every 3rd stroke. Breathing every stroke isn't efficient and breathing every 4th is hard to maintain.
Get a pull bouy, stick it between your legs and swim. This helps your style SO much. You become aware of how much your body twists when you breath (you can work on keeping your hips still) plus it makes you aware that so much of your power comes from your shoulders, rolling them and gliding. There shouldn't be any thrashing. Kicking doesn't really add speed.
Brixton rec has kickboards and pull bouys available for use.
I've been trying to keep off my knee since a physio apt last monday. This means no gym and more swim!
Mornings are best.
Found this too - seems like a good read
http://books.google.co.uk/books?id=VwiXl-ZzbT8C&pg=PA4&lpg=PA4&dq=difference+backstroke+kicks&source=bl&ots=Ay8IF8t__z&sig=Rm1QSbxU1wuTa4eEoMMndCeYedM&hl=en&ei=a3XqTMSeJYaKhQfm_cgP&sa=X&oi=book_result&ct=result&resnum=2&ved=0CCMQ6AEwAQ#v=onepage&q&f=false