In its interim results for the half year ending 30 June, Derwent London said: "the outcome of the EU referendum may lower activity", and reduced its estimate of rental growth from between five and eight per cent down to between one and five per cent.
The company's share price was down just over three per cent after the announcement.
However, Derwent said the first six months of lettings was the highest half-year in its history, letting 267,700 sq ft of space, generating £16.7m.
11 August 2016 @ 9:30amDerwent London (DLN)
Since 30 June, Derwent has let 112,600 sq ft, worth £4.6m, and the company said its "middle market" focus and good design means it is "well placed" in the current economic climate.
John Burns, Derwent's chief executive, said the company has secured "record lettings" in the first half of the year, adding that "this momentum has been maintained into the second half".
Robbie Raybe, chairman, commented: "It is early days since the EU referendum but London remains a major global city with significant attractions and potential for the future."
He said the company's "flexible and dynamic business model" would enable it to respond to the changing economic environment after the Brexit vote.