British expats have lost their High Court battle over the right to vote in the European Union referendum.
Expats who have lived outside of Britain for more than 15 years cannot vote in UK elections.
The legal challenge was brought by 94-year-old Second World War veteran Harry Shindler, who lives in Italy, and lawyer and Belgian resident Jacquelyn MacLennan.
Mr Shindler told ITV News he was "disappointed but not surprised" by the High Court decision.
Lawyers acting for the ex-pats confirmed they will seek leave to appeal directly to the Supreme Court.
Mr Shindler said: "It's very sad but it's not really surprising. We now have to look at where we can go from here.
"It's not over yet. We have lost the battle in the past but at the end of the day we won the war."
Mr Shindler appealed directly to Prime Minister David Cameron to act to get legislation through Parliament before the vote - the Conservatives pledged to scrap the 15-year rule in their election manifesto.
"At this last minute, if he wants to save the country from coming out of Europe, he could arrange for an amendment to the referendum bill and get that through Parliament," he said. "If we get our vote we will save England."
Those bringing the case argued they were being illegally denied the chance to vote and asked two judges sitting in London to declare Section 2 of the EU Referendum Act 2015, which establishes "the 15-year rule" for overseas electors, unlawfully restricted their right to freedom of movement under EU law.
But Lord Justice Lloyd Jones, sitting with Mr Justice Blake, ruled section 2 did not restrict their rights and rejected their application for judicial review.
According to law firm Leigh Day, acting for the ex-pats, up to two million British citizens living in other EU countries could be barred from taking part in the June 23 in/out vote.
Richard Stein, from Leigh Day, said: "We now intend to take the legal battle to the Supreme Court, the highest court in the country, so that all British citizens living elsewhere in the EU can be part of the democratic process to vote in this referendum, which will have a very real impact on their lives.
"We believe that there is precedent for fast-track legislation being put through Parliament in a matter of days in response to court judgment, so there would be no need for the referendum to be delayed if the Supreme Court rules in our favour.
"Since this is a vote in a referendum rather than in an election there is no need to link the votes of Britons in Europe to any particular constituency in the UK. Possession of a British passport should be enough."
A Cabinet Office spokeswoman said: "The Government welcomes the ruling of the High Court in this case.
"The franchise for the EU referendum was debated, considered and agreed by both Houses of Parliament and is enshrined in law."