Democracy watchdog the Electoral Commission has opened an investigation into EU referendum spending by the Vote Leave campaign.
As well as looking into whether the main pro-Brexit campaign exceeded spending limits and entered an incorrect return, the Commission will also investigate donations made by Vote Leave to student Darren Grimes and Veterans for Britain.
The announcement of the inquiry came as anti-EU millionaire Arron Banks, chair of the separate Leave.EU organisation, threatened legal action against the Commission over its investigation into his Brexit campaign.
Electoral Commission figures show that Mr Grimes received donations totalling £625,000 from Vote Leave, which - along with £50,000 from an individual donor - allowed the 23-year-old to spend £675,000 on the BeLeave social media campaign to encourage young people to vote to quit the EU in last year's referendum.
Veterans for Britain also received a donation worth £100,000 from Vote Leave in the run-up to the June 23 2016 vote.
Vote Leave reported spending totalling almost £6.8 million on the referendum, bringing it close to the £7 million limit for the designated lead campaign. Registered campaigners like Mr Grimes and Veterans for Britain were permitted to spend £700,000.