Two judges rejected accusations by multi-millionaire Sir James Goldsmith's party that it had been "unfairly and unlawfully" limited to one five-minute broadcast.
They dismissed applications for judicial review brought against the BBC and the Independent Television Commission, which had upheld ITV's decision not to allocate more air time.
Lord Justice Auld, sitting with Mr Justice Popplewell, said: "For reasons that we shall give in reserved judgments next week, both of these applications are refused."
Asked if there would be an appeal, a Referendum Party spokesman said: "We are naturally disappointed, but we will consider the judges' reasons and then discuss with our legal advisers the next stage."
Anne Sloman, the BBC's chief political adviser said: "We are absolutely delighted that in reaching their judgment their lordships acknowledged that our decision-making process was entirely proper and fair."
During the one-day hearing, Geoffrey Robertson QC, for the Referendum Party, argued it was a serious contender in the race to form the next Government. It was fielding 547 candidates, yet the three main parties had been given up to 10 times as much air time.