delirious:
If you owe money due to a missed payment your supplier is entitled to object to a transfer. If the money is owed only because the direct debit is too low, the supplier is not entitled to object to the transfer, but you would need the pay the debit soon after the switch.
The electronic gizzmos you mention are irrelevent because they use a piffling amount of power, even the maligned sky box. Things that get hot hot hot are the things that use power. Surely you have hot water, a kettle, a toaster and a cooker. Probably the storage heaters are using 50% of your consumption. £100/month is a lot but not hugely excessive for an electrically heated house. The real issue is not the gizzmos but how many storage heaters, how well insulated is your home and what do you do when the storage heaters run out heat in the early evening.
You need to get a handle on your consumption by reading the meters more often, but mainly in the winter period. If you don't its just guesswork.