The unofficial Brexit campaign group Leave.EU has been fined £70,000 ($95,000) for exceeding a limit on expenditure, the British elections watchdog the Electoral Commission has said.

Leave.EU — the group backed by former Ukip leader Nigel Farage and anti-EU doner Aaron Banks — has been the the subject of a probe into funding and spending during the UK’s European Union membership referendum.

The Brexit vote saw 17.4 million people — some 51.9% of the UK electorate — vote to leave the EU in the 23 June 2016 referendum.

Leave.EU did not include “at least” £77,380 in its spending return, “thereby exceeding the spending limit for non-party registered campaigners by at least 10%,” the watchdog said.

The commission said in a statement:

The investigation concluded that Leave.EU incorrectly reported what it spent at the EU referendum. It exceeded its statutory spending limit and delivered incomplete and inaccurate spending and transaction returns.

The commission also considers that the unlawful over-spend may well have been considerably higher than that.

Bob Posner, the Electoral Commission’s director of political finance and regulation, said:

These are serious offences. Leave.EU exceeded its spending limit and failed to declare its funding and its spending correctly.

Banks, the founder of Leave.EU, cast doubt on the Electoral Commission’s impartiality and said it was full of EU supporters.

The Electoral Commission is a Blairite swamp creation packed full of establishment Remoaners.

We view the Electoral Commission announcement as a politically motivated attack on Brexit and the 17.4 million people who defied the establishment to vote for an independent Britain.

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The Electoral Commission went big game fishing and found a few aged dead sardines on the beach. So much for the big conspiracy!

What a shambles, we will see them in court.

Meanwhile, the watchdog said it had found no evidence that Leave.EU received donations or paid-for services from Cambridge Analytica, a political consultancy at the centre of a storm over how Facebook data was used in political campaigns.

It said:

The investigation found no evidence that Leave.EU received donations or paid-for services from Cambridge Analytica for its referendum campaigning and found that the relationship did not develop beyond initial scoping work.

Leave.EU and Cambridge Analytica had previously denied working together on the Brexit campaign. Rival group — Vote Leave — was the officially designated Brexit campaign group during the referendum.