Cheers for the responses guys. After all my yarns about quick release sheaths being flimsy the cheap knife & rubber sheath I bought off trademe broke the first time I tried to put it into the sheath. The rubber tab you put over the tank banger failed. No not in the water, it literally broke in my kitchen the first time I tried it (best be getting a refund). Funnily enough the same tab failed on my old knife but only after about 5 years of abuse. I don't actually think you can buy a high quality knife in the old sheaths anymore.
The old style sheath/knives I mean: http://www.splash.co.nz/shop/Scuba+Prod ... P+330.html
Yeah I have heard UK knives are a bit overpriced though.
That Wenoka big squeeze knife looks perfect for both scuba and spearfishing but I can't find it anywhere but ebay.