Shares in UK energy groups tumble as Treasury plans windfall tax

Shares in some of Britain’s biggest power companies fell sharply on Tuesday as Rishi Sunak drew up plans for a windfall tax on the energy sector to help offset spiralling domestic fuel bills.

The chancellor is rushing to complete an emergency energy package to offer relief to households struggling with a spiralling cost of living crisis and the prospect of an £800 increase in fuel costs in the autumn.

Drax, owner of the UK’s biggest…