Note that fixed tariffs available now are MUCH higher than variable tariffs AND are also much higher than Ofgem's Price Cap as the Cap does not apply to them.
The "standard" domestic dual fuel customer proscribed by Ofgem uses 2,900 kWh electricity and 12,000 kWh gas per year, and the Price Cap from 1st October for this usage is £1,277 for a default variable tariff paid by direct debit.
Energy companies must charge less than £1,277 for the default variable tariff (and this cap should last until 31/03/22), but they can charge much more for fixed tariffs. For example Octopus, who are historically one of the cheaper major suppliers have their variable tariff set at £1,201, but their current fixed tariff offer is set at £1,542.
My cheap fixed tariff expires at the end of September, and my options are a 33% rise to move to a variable tariff, or a 66% rise for a new fixed deal.