Derwent's stock, which has lost about 18 percent of its value up to Wednesday's close since the Brexit vote, fell as much as 3.5 percent to 2721 pence at 0915 GMT on the London Stock Exchange.

Concerns have risen that prices for commercial properties may fall after the vote, with some investors worried that international retailers and banks may move some operations to other EU locations, hurting demand for property.

Derwent's warning follows similar statements by larger players in the field such as Countrywide Plc, British Land Company Plc and Hammerson Plc.

Derwent said on Thursday it saw its highest half-year letting activity ever in the first-half of 2016, and now expects full-year rental growth at 1-5 percent.

The company had earlier forecast full-year rental growth of 5-8 percent.

However, Derwent said it was still "well-placed" to weather the uncertainty and added that only 2.3 percent of its rental income in June came from London's financial sector.

"It's just a question of saying that things may slow down, though we have no evidence of that at the moment. We are in uncharted waters and based on our experience, it's just better to be a little more cautious," Derwent chief executive John Burns told Reuters.

At least three analysts kept their 'hold' rating on the stock noting that the company's letting activity momentum was maintained after June and that the average lease length for Derwent was 6.8 years.

Burns also said Derwent's cut on the rental growth forecast was not too severe and that the company had not seen any rental renegotiation after the Brexit vote.

(Reporting by Vidya L Nathan in Bengaluru, Editing by Sunil Nair)

By Vidya L Nathan