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 watchdog will also investigate donations made by Vote Leave to student Darren Grimes and Veterans for Britain.

The announcement of the inquiry came as millionaire Arron Banks, chairman of the separate Leave.EU organisation, threatened legal action against the commission over its investigation into his Brexit campaign.

Electoral Commission figures show 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 received a donation worth £100,000 from Vote Leave in the run-up to the vote.

Vote Leave reported spending totalling almost £6.8 million on the referendum, bringing it close to the £7m limit for the designated lead campaign. Registered campaigners such as Grimes and Veterans for Britain were permitted to spend £700,000.

Meanwhile, insurance tycoon Banks said he would seek a judicial review of the Electoral Commission’s decision to launch investigations into Leave.EU unless it gave details of its sources within 21 days.

He issued the threat after the commission said its investigation was being delayed because the Brexit campaign group had failed to hand over requested information.

The commission is looking into the alleged undeclared provision of services to Leave.EU by data firm Cambridge Analytica. It is also separately looking into whether Banks was the “true source” of three loans worth £6 million on non-commercial terms to Leave.EU, and whether Better For The Country Limited was acting as an “agent” when it donated £2.3m to five registered campaigners.