The pair have immediately regeared a lease with BSI Management Systems on around 90,000 sq ft for another 10 years. BSI will now remain in the building until 2025.

An agreement with BSI so soon after the purchase will be viewed as a coup by the pair. The deal represented a net initial yield of around 10%, but BSI’s existing lease brought in around £22/sq ft, a low rent for the area.

The regeared lease involves a refurbishment of the building and a rent rise to the mid-£20s/sq ft.

BSI Group chief executive Howard Kerr said: “The BSI Tower is the group’s home and this deal gives us stability and certainty of knowing that we will stay in Chiswick for the foreseeable future.”

Japanese computer game developer Konami, Actelion Pharmaceuticals and media firm IDC are among the tower’s other tenants. Frost Meadowcroft and Savills have been appointed to

market the remaining 30,000 sq ft.

Canmoor has entered into office ventures in the past, notably in Reading and Denham in partnership with Korine Property Partners and the Widewater Trust respectively.

But the company has historically been known as an industrial developer and asset manager. This latest success in the office market could raise the prospect of similar deals and broaden the spectrum of the firm’s future investment targets.

It is the second joint venture between Canmoor and Harbert, after the pair bought four multi-let industrial estates totalling 2.1m sq ft from Segro 18 months ago for £104m.

US-based Harbert has been particularly active in the UK in recent months. The group bought a 350,000 sq ft warehouse in Crick from Tesco for £10m in August, and sold an £82m distribution portfolio to London & Stamford Property earlier this month.

The sale marks the first disposal by Carlyle Group from the £670m Thames portfolio, which it bought in July this year.