@fran1 Did they say what the £174 was for? For example, someone who was on a 2 year fixed-rate tariff that ended this year would see a huge jump in cost because prices have risen a lot over the last 2 years.
Ae you looking at the end of a fixed-term deal? If you are, simply take the notice as SP letting you know how much you'll be paying next year and either change your tariff or switch to another supplier that offers you a better deal. If you're not, and don't like the reason SP are giving for the price rise, switch anyway.
It really is a no-brainer,
@fran1 Your bill does look high, but electric heating is very expensive and I suppose your brother has gas central heating?
It is quite possible to have an electric bill of 1400, take a close look at how you heat the house and try to use supplementary heat like burning wood or coal, or getting a calor gas heater. By all means try citizens advice, a lot of people do that and find they can reduce their bills.
Just a word about portable gas heaters. I find them a bit of a false economy. Apart from the obvious safety issues of having a fire on wheels in the house, it's recommended a window is left open in rooms they're used to allow carbon monoxide to clear, and that tends to negate the reason for having the heater.
Plus, after buying the heater, paying the initial cylinder rental and paying for the actual gas, a 15Kg cylinder only tends to last 4 or 5 weeks if used every day for more than a couple hours, so it'll be year three before a saving is seen, and even then the annual cost is still going to be about £150.