Buying properties with leases nearing their end is risky because tenants can move out, leaving the landlord without income.

Yet, the amount of central London workspace for rent was at its lowest in seven years, Deloitte Real Estate said in May, reducing the risk of vacancy even as rents rose.

Investors including Blackstone Group, the world's biggest buyout firm, and London developer Workspace Group have been buying short-lease buildings to take advantage of the trend.

The gains for short-leased office space showed that "growing occupier demand for space in London is encouraging investors to look for assets that they can actively manage to generate higher income returns upon tenant expiry", said Phil Tily, a managing director at IPD.

The cost of leasing office space in central London had risen 8.5 per cent in the 12 months to June, almost twice the increase a year earlier, IPD said.

Workspace bought Vestry Street Studios, a converted warehouse in Shoreditch district, for £12.6 million (HK$162 million) in May.

One of the main attractions was that the leases were close to expiring, chief executive Jamie Hopkins said in a call with analysts.

"We can get in there and quickly drive that rental model up," Hopkins said.

Blackstone bought the Adelphi Building near London's Trafalgar Square last year for about £260 million in part because a lease on half the building ended last summer.

The New York-based buyout firm is spending about £30 million refurbishing the property to attract tenants, according to occupancy services provider ISG.

The IPD data compared the performance of the top 25 per cent of office properties by unexpired lease term with the same percentage where occupiers are closest to having the option of leaving.