Apparently you can get trip switches that plug into the fuse box, where your fuse carriers currently sit - can't remember how much they cost, but my dad has been nagging us to get them for a while (he's seen them in Focus DIY, and I'm sure they are probably available from Screwfix). Obviously the ideal situation is to get an RCD box, but this could be be a good interim measure.
Suprising how we take electricity for granted, I still think (passed statistics) that there have been no fatalities where an RCD has been installed in an electrical installation.
Alan (NICEIC electrical domestic installer)
see:- https://www.NICEIC.com for electrical safety advice
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