The firm has already completed demolition work at Brunel Building in Paddington, however a decision later in the year could delay the scheme.
In an interim results statement, Derwent said: “There is some flexibility with the timing of the Paddington scheme, which could be slowed down or even deferred if necessary.
“We have various options, and so we will be monitoring occupier demand closely in the next few months to see whether to continue at the current pace, slow down or reduce development expenditure.
“A decision does not have to be made until later in 2016.”
The Brunel Building was originally set for completion in H1 2019.
The project was estimated to cost between £50-100m.
Derwent said the EU referendum result was likely to lead to reduced demand in the central London office market.
Despite this, the firm insisted that London will continue to appeal to a range of international and domestic occupiers.
Robbie Rayne, chairman at Derwent, added: “It is early days since the EU referendum, but London remains a major global city with significant attractions and potential for the future.
“Derwent London has a flexible and dynamic business model and a strong balance sheet with low leverage, which enables us to respond to changing economic conditions.”