Great Portland has agreed to sell Rathbone Square, a mixed-use development that houses Facebook's new London headquarters, to German rival WestInvest Gesellschaft and asset manager Deka Immobilien for 435 million pounds.
The sale is at a 4 percent discount to the asset's September valuation.
Although Britain's property investment market has been more resilient than expected as the pound's slide has attracted overseas investors, analysts have warned values could fall this year due to uncertainty over Britain's exit from the EU.
Investors have managed to secure about a 3 percent discount on offer prices on the 8 billion pounds of UK commercial property sold since the June vote, according to commercial real estate company Cushman & Wakefield.
Great Portland Chief Executive Toby Courtauld told analysts the deals market for larger properties was less liquid, with buyers asking for lower prices given the higher risk in the current market.
"(For large projects), there aren't as many buyers around. That's what we've felt. It's a scale thing in a world with slightly less uncertainty," he said.
Great Portland had to offer a discount on Rathbone Square, its largest development scheme ever, despite about 57 percent of the development having been rented by Facebook, raising concerns that the rest of its portfolio could see a negative re-evaluation.
"The pricing of the asset with an uber prime covenant of Facebook... is disappointing," Jefferies analysts wrote. "It doesn't give the bulls the excuse that Brexit was just a passing storm...and everything in the garden is rosy."
In November, Great Portland, whose portfolio is dominated by offices, cut its full-year rental growth forecast.
The company said it expected to remain a net seller of property this year and would return any surplus cash if it did not find investment opportunities for about 600 million pounds it would have after the deal closed.
Courtauld told analysts Great Portland had backed out of some potential purchases as the "pricing didn't work".
It intends to return about 110 million pounds to investors via a special dividend and undertake a share consolidation.
(Reporting by Noor Zainab Hussain in Bengaluru; Editing by Sunil Nair and Susan Thomas)