London based real estate investment firm Castleforge yesterday celebrated the topping out of One Golden Lane, its 120,000+ sq ft Grade A office development adjacent to the iconic Barbican Centre in the City of London.  

The ceremony, attended by senior City of London Corporation officials including Gwyn Richards, Planning and Development Director, marked the structural completion of the building’s 12th storey, set for completion in Q2 2026.

Located four minutes from the Elizabeth Line at Farringdon, One Golden Lane forms part of Castleforge’s broader pipeline, which will deliver over 1,000,000 sq ft of Grade A space in the next 24 months, including a landmark redevelopment at 75 London Wall, 55 Mark Lane and Cannon Bridge House.

The milestone comes at a critical time for Central London’s increasingly supply-constrained office market, where Grade A vacancy rates have fallen to historic lows of just 2.1% in prime City locations.

As return-to-work mandates become commonplace, businesses are increasingly competing for amenity-rich, ESG compliant spaces, fuelling rental growth across the City.

Central London office take-up is running 30% ahead of last year, with Grade-A space accounting for over two-thirds of demand.

Helping to address this supply-demand imbalance, One Golden Lane will offer over 120,000 square feet of flexible, modern office space, including 7,000 square feet of terraces and roof gardens designed by Chelsea Flower Show Gold Medallist Andy Sturgeon,

Further amenities include a statement double-height lobby and café, multiple terraces with city views, and 3,900 square feet of wellness and community space, designed to support modern working patterns.

The Grade II listed development, originally designed by Tate Britain architect Sidney Smith, retains its heritage features including the 1896 façade while its newly completed 12th storey offers commanding views across the Barbican—demonstrating how historic buildings can be transformed into best-in-class modern workspaces.

Additionally, One Golden Lane pioneers sustainability in construction, retaining 95% of the existing building and becoming the first London scheme to reuse over 5 tonnes of reclaimed steel from the same site.

The development is targeting Net Zero Whole Life Carbon and BREEAM ‘Outstanding’ certification, with integrated urban greening throughout and 100% renewable energy powering operations.

Michael Kovacs, Founding Partner of Castleforge, said: “The topping out of One Golden Lane represents more than a construction milestone- it’s a tangible response to London’s acute shortage of Grade A office space. The development reimagines the office headquarters for the modern-day workforce and has been created to give people an exceptional working environment, designed to be sustainable in every way. With prime vacancy rates in core locations sitting as low as 2.1%, developments such as this are essential to maintaining London’s competitiveness as a global business destination.”

Tom Sleigh, Chairman of the City of London Corporation’s Planning and Transportation Committee, added: “One Golden Lane exemplifies what we want to see across the Square Mile—quality office space that respects our heritage while embracing modern sustainability. Projects such as this reinforce the City’s position as an international commercial hub and a fantastic place, not just to work, but also live and visit.”

The development has been delivered directly by Castleforge’s in-house investment and asset management team, with construction by Midgard and financing from Cheyne Capital and Apollo.

This development, along with the balance of their London portfolio positions Castleforge as a significant contributor to the city’s office supply at a time when institutional capital is returning to the sector, with investment volumes in the first half of 2025 running 60% higher than the equivalent period last year.