Investigations have been launched into the spending by both side in Britain's EU referendum.

The Electoral Commission there has announced probes of the 'Stronger In' and 'Vote Leave' campaigns.

It has revealed figures showing more than stg£32m (€37.8m) was spent on the campaign, making it the most expensive referendum in British political history.

Details of groups that spent stg£250,000 (€295,000) or more show the major Remain campaigns spending almost stg£16.2m (€19.1m), compared with stg£11.5m (€13.6) for Leave.

When combined with details of smaller spenders released last November, this means the Remain campaign outspent Leave by a margin of stg£19,070,566 (€22,579,358) to stg£13,436,241 (€15,908,299).

The Leave side received stg£16.4m (€19.4m) in donations, compared with Remain's total of stg£15.1m (€17.8m). The two lead campaigns also received stg£600,000 (€710,311) each of British taxpayers' money to help fund their campaigns.

After an initial inspection of spending returns from both sides, the commission found that neither Stronger In nor Vote Leave had submitted all of the necessary invoices and receipts to back up their accounts.

Details of suppliers were missing for some payments, the watchdog said.

Its director of political finance, Bob Posner, said: "It is disappointing that some campaigners, including both lead campaigns, 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."

The commission is 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 begin investigations.

A Vote Leave spokesman said its accounts were approved by external auditors and that it believes it "fully complied" with spending regulations.

He said: "Vote Leave will fully co-operate with the Electoral Commission's investigation.

"When we handed in our return on December 23rd, 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."