But I'm nervous for my underwater camera so I wondered what if would be reliable? I do not want to spend much money (as in nothing more than £ 400) Any suggestions?

Found for ya! It's $ 119 in http://www.primescuba.com/canon-eos-450d-slr-digital-camera-underwater-housing.html've been diving for some years now, and had the same concerns with my camera. It's definitely always a better choice if that works with your specific camera – this ensures that it is completely tight waterproof. Enjoy, and happy diving! Your photos will look great!

Arctic 2002: Breathtaking Under-Ice Diving Photography