Lord Foster has agreed to sell a stake in his practice to 3i and to appoint a chief executive. Financial Times

The 71-year-old designer of 'the Gherkin' said he was looking to plan 'a future beyond my own life' for his architecture practice, Foster & Partners as it celebrates its 40th anniversary with a deal that is understood to value the business at about £300m.

'How do you bring to bear the foundations for something that builds on that for the next 40 years and beyond?' said Foster.

While the founder will take out some cash, the new capital is primarily aimed at funding an expansion plan, whereby 3i said it wants Foster & Partners to double in size.