Chief Executive Toby Courtauld said: “The referendum result has had a negative effect on business confidence in London which will likely result in lower economic growth.
“As a consequence, we can expect London’s commercial property markets to weaken during this period of uncertainty.”
Great Portland Estates is currently on site at five schemes and has two uncommitted schemes in the pipeline which “could start in the next 18 months”.
At Oxford House on Oxford Street the firm has planning approval for an 88,200 sq ft major mixed-use refurbishment.
As part of the letting at Rathbone Square, Facebook has a right of first offer to pre-let all the anticipated 55,700 sq ft of office space.
At Hanover Square, W1, demolition work is currently underway on the western side of the site.
The firm said: “These limited works will give us the option, should the market be supportive, to accelerate the construction programme for the wider scheme ahead of delivery of the station structure by Crossrail in 2018.
“Beyond our near-term schemes, GPE’s well stocked development pipeline for the next cycle includes a further 14 uncommitted projects (1.4 million sq ft). These properties are income producing today with an average lease length of 3.9 years.”