TOKYO, June 24 (Reuters) - Japan's Nikkei gave back earlier modest gains and fell into the red amid nervous trading, as votes were counted in Britain's referendum on EU membership.
The Nikkei was down more than 2.5 percent. The index had gained early after polling firm YouGov said the campaign to keep Britain in the EU appeared to be ahead, but the Nikkei reversed course when the "leave" camp began to take frequent leads in the vote count.
The Topix index was down 2.4 percent. (Reporting by the Tokyo markets team; Editing by Eric Meijer)