The investment comes as Britain's new Labour government tries to drum up billions of pounds in foreign investment into the country as it marks 100 days in office and welcomes global business leaders for the Oct. 14 summit.
"We are creating the conditions for businesses to thrive, and our International Investment Summit will be a springboard for every part of the UK to be an engine of innovation and investment," British Prime Minister Keir Starmer said in a statement on Thursday.
Around two-thirds of Iberdrola's investment would go into power transmission and distribution networks, the company said.
Britain's energy system operator has said some 58 billion pounds of investment will be needed in the country's power grids to handle the huge increase in renewable power projects expected as Britain strives to meet climate targets.
The Labour government's plans to decarbonise the electricity sector by 2030 also require a big increase in renewable power capacity such as wind and solar.
"The clear policy direction, stable regulatory frameworks and overall attractiveness of the UK are leading us to double our investments for 2024-28," Iberdrola Executive Chairman and Scottish Power Chairman Ignacio Galan said.
Galan will join Starmer in Scotland on Friday to make the announcement, where the British leader will also meet with regional mayors and first ministers in a Council of Nations and Regions meeting focused on growth and investment.
