After looking for a cheap underwater housing for 100 quid or less, I thought it must be a typo to find this genuine Casio one for 24 quid delivered! I ordered it a week or two ago, and I just got the email to say it had been dispatched. The RRP is 199 Euros. It's the real deal with a max depth of 40 metres.
Apparently works with: Casio EXILIM Zoom EX-Z700 * Casio EXILIM EX-Z600 * Casio EXILIM EX-Z500
More info here: http://www.digideep.com/english/underwater/photo/housing/Casio/EWC-70/8/2488