Small-cap oil and gas companies which operate in the North Sea have tumbled after the Labour Party confirmed its plans to create a publicly-owned clean energy business funded through windfall taxes.

As well as creating Great British Energy, Labour has promised to not award any new licences to oil and gas firms in a bid to "ensure a phased and responsible transition in the North Sea”.

As a result, shares in Serica Energy PLC dropped 9.5%, Deltic Energy PLC fell 18%, Jersey Oil and Gas PLC tumbled 19.5% and Ithaca Energy PLC slipped 3%.

Cleantech companies also traded lower at the prospect of new competition, with the likes of Inspirit Energy Holdings PLC losing a quarter of its market capitalisation.

Keir Starmer talking on the topic today said: "We want the oil and gas companies to pay fair tax on the massive profits that they’re making."

Shell and BP both held flat in reaction.