A proposed legal challenge to the Electoral Commission's decision to make Vote Leave the official Out campaign in the EU referendum has been abandoned.
UKIP donor Arron Banks reacted angrily to news that the group he was backing had not been selected, claiming the decision was "corrupt".
But he said he had decided not to seek a judicial review after talking to UKIP leader Nigel Farage.
Mr Farage has said he will campaign with any group that wants an EU exit.
Mr Banks' Leave.EU group was affiliated to Grassroots Out (GO), the group that lost out to Vote Leave.
Announcing its decision on Wednesday, the Electoral Commission said Vote Leave had "better demonstrated that it has the structures in place to ensure the views of other campaigners are represented in the delivery of its campaign"
"It therefore represents, to a greater extent than 'Go Movement Ltd', those campaigning for the 'Leave' outcome, which is the test we must apply," it added.
Mr Banks signalled his intention to launch a legal challenge immediately after the news that Vote Leave had won the official designation, and said it could delay the referendum - taking place on 23 June - until October.
After consulting lawyers, he said: "What is clear now is that if we were to pursue a judicial review, according to legal experts, we would win."
But explaining the group's change of heart, he added: "But this is a time to take a step back from the matter, and after consulting with leading campaigners on this issue, including UK Independence Party leader Nigel Farage - we have decided to show the public how this process was stitched up, but not to pursue the judicial review any further."
He said it was time to "turn our collective guns on the real opponents" in the referendum campaign - those campaigning for Britain to remain in the EU.
"We will be pursuing this campaign with vigour - and we'll have some fun with it along the way," he said.
Britain Stronger In Europe, led by former Marks and Spencer boss Lord Rose, is the lead campaign for the Remain side.