The company, which develops properties in areas such as London's popular West End, said it expected rental values to be between down 3 percent and up 2 percent, against a previous estimate of flat to down 5 percent.

Derwent's confidence was underpinned by strong demand from tenants in the technology, media and telecoms (TMT) sectors, and its limited exposure to financial clients, which accounted for just 2.8 percent of its rental portfolio, its head said.

"We're just letting extremely well," Chief Executive John Burns told Reuters. "We've seen a lot of interest largely from TMT people. So there's no let up. It's very strong."

The London office market has seen rents slip slightly and vacancy levels rise in the aftermath of the Brexit vote, which raised concerns that financial jobs will move elsewhere in the EU and that some tenants may defer investment decisions.

This has lead some developers to reduce the amount of speculative office space they are building without a guaranteed tenant, while Derwent cut its 2016 rental growth forecast and lowered the value of two London developments.

The company said on Thursday it had achieved a record six months of lettings totalling 23.4 million pounds, on average 0.5 percent above estimated rental values at December 2016.

"We believe Derwent remains in a good position to continue to navigate market uncertainty, with low financial risk and an office portfolio less exposed to new supply and financial services occupier risk," Liberum analyst David Brockton wrote.

The company's shares were up 0.3 percent at 2,813 pence by 0843 GMT.

Derwent posted a 0.9 percent rise in net asset value to 3,582 pence per share for the six months to June 30 and hiked its first-half dividend 25 percent to 17.33 pence.

Derwent, which had a portfolio worth about 4.8 billion pounds as of June 30, also said it would advance with its next major development at Soho Place, above Tottenham Court Road underground station.

Burns said the development, which would include offices, shops and a new theatre, had already attracted interest.

"We're finding a lot of people approaching us ... and putting their name out as a possible tenant," he said, adding that the talks were with a "very wide spread of big companies" outside the financial sector.

(Reporting by Esha Vaish in Bengaluru; Editing by David Holmes)

By Esha Vaish