CAMPAIGNERS spent more than £32 million fighting last year’s EU referendum, according to accounts published yesterday, but discrepancies on both sides have led the Electoral Commission to launch investigations into their finances.

The watchdog said they would be looking into the returns of both lead campaigns in last year’s EU referendum – Stronger In and Vote Leave – and that neither side had submitted all necessary invoices and receipts to back up their accounts.

The Leave side received donations of £16.4m, just slightly more than Remain’s £15.1m. The Remain campaign outspent Leave by more than £5m, through spending £16.2m, compared to £11.5m for Leave.

When combined with details of smaller donors released last November, this means the Remain campaign outspent Leave through donations totalling £19,070,566 compared to Remain’s total of £13,436,241. The Commission has also opened an investigation into missing details of suppliers, invoices and receipts in the Liberal Democrats’ return, as well as into individual campaigner Peter Harris, who delivered his spending report late and without the required audit form.

The Commission is also undertaking further examination of apparent discrepancies in returns submitted by the European Movement, Ukip, Labour Leave, Grassroots Out and Conservatives In, before deciding whether to open investigations.

The Commission’s director of political finance, Bob Posner, said: “It is disappointing that some campaigners, including both lead campaigners, appear to have not fully reported all their spending as they should have.

“Missing spending details undermines transparency and makes the returns harder for the public to understand. Where it appears campaigners have not fulfilled their legal obligations, we have begun and will continue to take action to deal with this.” A Vote Leave spokesman said: “Vote Leave’s accounts were approved by external auditors and we believe we have fully complied with all the spending regulations for the EU referendum.

“Vote Leave will fully co-operate with the Electoral Commission’s investigation. When we handed in our return on December 23 we realised that we had submitted it with excess spending that did not need to be reported, so it was therefore amended.

“We were also missing a handful of invoices from suppliers but these have since been provided.”

The receipts released yesterday showed that the Leave Campaign’s NHS bus cost £90,000 to hire for the campaign.

The coach was emblazoned with the claim that the UK sent £350m a week to the EU and that the money could instead be spent on the NHS. The figure was discredited by the head of the UK Statistics Authority as it didn’t take into account the money Britain got back from Europe in its rebate. Campaign chiefs have since distanced themselves from the promise.

Other costs revealed in the Vote Leave accounts include a £200,000 insurance bill for underwriting a Euro 2016 competition which offered £50m to anyone who correctly predicted the outcome of every match at the football tournament. Nobody won, but £50,000 was paid out to the person who came closest.