Unless I've missed it, you don't give the split between what your bill is for daytime electricity and cheap rate overnight electricity i.e. what you use on night store heaters, running your washing machine, dishwasher, immersion heater, etc. (you do run them overnight I hope, with time clocks). Comparing the two figures would show you where the bulk of your costs are coming from. There's not a lot of point in trying to economise during the day if it's the night stores that are making up the bulk of the bill. Do your night stores have a 4pm boost, because IIRC that can be at daytime rates and can be really expensive.
We're also in Cornwall, on E7, Southern Electric, paid by DD. 3 bed bungalow with dormer room, DG and loft insulation but no cavity wall insulation, just two of us home all day (retired). Gas CH supplemented by very occasional electric heating (the odd fan heater on in the autumn evenings before the gas CH is switched on), electric cooking (hob+oven, microwave), one fridge, one freezer. Dishwasher run every night, washing machine for clothes say twice per week (no tumble drier), immersion on every night, all three on timers for E7. We have one night store heater but haven't used it for a couple of years (used to have three but I took the other two out years ago). A few low-energy light bulbs, but some filament ones also. Excess hot water from the kettle is stored in a big thermos flask for next time (must save a penny or two!).
FWIW, our total electricity bill for May 2009 to May 2010 was £642, less about £30 for DD discount. The units/cost breakdown between cheap rate and daytime rate was 2773 units/£151 night rate against 3116 units/£491 day rate. Night energy rate currently (oops, sorry!)
5.45p/unit, and day rate 18.83p/unit for first 1000 units/year then 14.33p/unit thereafter.