Singapore investment firm GIC is buying a multibillion dollar stake in a mega-office complex in London's main financial district, adding to its portfolio of prominent properties globally.

It is acquiring private equity firm Blackstone's 50 per cent interest in Broadgate, in a deal said to be worth over £1.7 billion (S$3.5 billion).

This transaction is believed to be GIC's largest-ever property foray in Europe, and is also its biggest-known investment this year, based on public announcements. Analysts said it is also one of Europe's biggest-ever office deals.

Broadgate is located near Liverpool Street station and is touted as a "world-class" office complex with a cluster of 17 buildings, shops and restaurants. The development spans 4.7 million sq ft on 12ha of land.

About 30,000 people work in the complex, which counts major banks such as UBS, the Royal Bank of Scotland, Deutsche Bank and Credit Agricole among its prominent tenants.

The asset has development potential, which GIC said it will be able to tap on to create more value.

It offers "an attractive combination of stable long-term income with the potential to create additional value," the investment firm said in a release on Tuesday.

GIC plans to add value through active management, repositioning of the office buildings and enhancing the retail and leisure offerings.

"These efforts will retain Broadgate's attraction to a broad range of international occupiers," GIC added.