Well, they're all nice ideas but none of them really solve my problem! The first one was close but I was looking for a safe that actually got fixed to the chassis directly rather than with a cable. Lets face it, cables are a cinch to snip with a set of bolt-cutters... O well, if I find anything I'll post it here but I suspect I'll be going down the DIY route and picking up an off-the-shelf safe from B&Q. (another UK chain store before anyone asks!)

Cheers!