I have a large 4 bed property - an extension was added in 2005 and I had some 6" Kingspan insulation put in to improve insulation on a flat roof and in the loft so these house is far better insulated - it remains nice and cool inside on very hot days and warm on cold winter days - you can tell, compared to other similar properties in the street that the snow or frost stays longer on our roof because it is better insulated - what is your house like? Mine used to be incredibly hot upstairs in the summer and freezing in the winter - the insulation changed all that.
I replaced all the 50W halogens on the house for LED lights - you also have to change the transformers that drive them. That must have busy about £500 but it paid for itself in 2 years.
I used the wireless energy monitor to find out what was using electricity. I found a hi-fi system was using the same on standby as it was when it was on. Importantly I worked out that a 20 year old fridge freezer was using nearly 1/3 of all my electricity - I had noticed it was humming into life noisily on quite a regular basis. The refrigerant leaks out and do the compressor was running fast more often than it should have been to try and keep the temperature down... I replaced the fridge freezer with the cheapest Bosch one from John Lewis (about £250 I think) and it's brilliant and paid for itself in about a year.
We turned the heating down 1 degree to 18C - it took a while to get used to it but after a couple of months we are fine with it.
My bills before an the office increases were £77pcm and they have gone up to £170pcm although by being more careful about using the oven less, not doing a rinse on the dishwasher (by buying better tablets) I reckon our bill can be knocked down to £148pcm. Radiators are off on bedrooms we don't use (2 kids have left uni now and never coming back!)
We don't have a tumble dryer - haven't had one for 20 years - we use an airer hanging from the ceiling in the utility room where the boiler is.
I'm sure it will be possible to find ways to bring your bills down. We don't leave anything on on standby - e.g. the printer, laptops, radio, TV. Definitely check your fridges and fridge freezers out - of you notice them humming and making a noise regularly they could be using quite a bit of electricity - basically flogging themselves to death trying to compress a tiny amount of refrigerant gas back into liquid. We have an electric shower in one bathroom that we never use now. I think twice about cooking anything that needs the oven.
Obviously check your loft insulation including your loft access. Keep doors closed to reduce airflow around the house.
£850 does seem a hell of a lot. Does your bill say you are in credit or debit? If your electricity meter a smart meter that is read remotely and automatically or have you been supplying real readings? If your bills are just based on estimated readings the bill could be out by a huge amount.