OP, I'm no expert on what activities and devices use the most lecky, but here are some suggestions and questions:
Boiling the kettle is very expensive. Try to limit it a bit (eg, everyone have drinks at the same time or put some hot water in a flask to use next time).
We keep showers very short indeed - no luxuriating in the lovely warm water! Just get clean and get out. Baths - I have a 'wartime bath' - not much water, and again, I wash and get out. Sounds miserable, I know, but if you're after thrifty tips...
Yes, I bet the dehumidifier and other devices which are on for a long time are adding up. Could you open windows sometimes (even just a bit) instead? We do this even when it's cold - just a bit of ventilation helps.
Washing: I know it's a nightmare with a family, but I always wear a least one t-shirt under a jumper and don't wash my jumpers very frequently. I always change into un-smart clothes when I get home from anywhere and this preserves my posher clothes for longer in terms of getting dirty and general wear. (I'm not in the least unhygienic, I assure you, but I was once shocked by an American friend who, I discovered, just put everything in the wash even if she'd only tried it on and decided not to wear it. )
We don't have lots of gadgets (don't have a tumble-dryer) so maybe we avoid expense a bit in that way - but I'm really not sure how much these things use. We try not to leave loads of things on standby, though (TV, radio etc) and turn them off at the socket when not in use. Also, I'm like the late Queen in that I'm obsessed with turning off lights in rooms we're not using.
Someone more knowledgeable is bound to say I'm wrong about some of these things...but this is just my offering!