The two expats had requested a judicial review of the 15-year rule, arguing that it was an arbitrary restriction of democratic rights and prevented UK expats from voting on matters that directly affect them.
"I am still waiting for the Government to tell us why British citizens in Europe can't vote in this referendum. The Government had agreed to scrap the 15-year rule before the Referendum Bill was passed, agreeing it was arbitrary and undemocratic," Shindler was quoted as saying by the channel.
The plaintiffs intend to lodge an appeal with the Supreme Court on Tuesday.
UK citizens are set to vote on June 23 in a referendum on the country's EU membership, after Prime Minister David Cameron and the leaders of the 27 other EU member states had reached a deal in February to grant the United Kingdom a special status within the bloc.
Some 1.3 million UK citizens live in EU member countries, according to government figures.