The Electoral Commission has reopened its investigation in the spending of Vote Leave campaign in the run up to the EU referendum.
Ahead of the vote in June 2016, the campaign paid £625,000 for bills allegedly run up by student Darren Grimes with a digital agency, the BBC has said.
Meanwhile, Veterans for Britain, received £100,000 from the campaign.
Vote Leave denies that it attempted to get around spending limits. And although the Electoral Commission initially accepted this, it has said that it now has new information.
The Good Law Project, a group of lawyers, have started legal action against the commission over its original decision to drop the probe claiming that it was not doing its job properly.
Jo Maugham QC, of the Good Law Project, said: 'We are 18 months after the referendum vote. It is extraordinary that only now is the Electoral Commission taking a serious look at whether the rules were complied with. And only in response to legal action.'
He added: 'The Electoral Commission has urged us to agree to drop our High Court case. We will consider this question carefully in the coming days.'
However, a source from Vote Leave told BBC News that the Commission was just giving into peer pressure from the Good Law Project.