LONDON (Reuters) - Multimillionaire Brexit donor Arron Banks wrote to Britain’s Electoral Commission on Thursday to imply he was the subject of a politically motivated investigation amid speculation that Russia may have meddled in the 2016 referendum vote.

FILE PHOTO: British businessman Arron Banks, who has funded the Leave.EU campaign, is seen during the opening day of the United Kingdom Independence Party (UKIP) annual conference at Doncaster Racecourse in Doncaster, northern Britain September 25, 2015. REUTERS/Andrew Yates/File Photo

In his letter, Banks said his campaign hired an accountant and an auditor, a lawyer oversaw all spending, and its returns were submitted after discussions with the election watchdog.

The Electoral Commission, which is already looking at whether Banks’ Leave.EU group received any impermissible donations, opened a new investigation last week into whether Banks was the true source of loans to a campaigner.

The announcement of the investigation came after a lawmaker from the opposition Labour Party asked the government to look into reports by advocacy group Open Democracy that the origin of some campaign funds was unclear.

Banks questioned why only his campaign group was being singled out for investigation and alleged all the commissioners at election watchdog support staying in the EU.

“The Commissioners are fully signed up ‘Remainers,’” he said in the letter. “It really is quite incredible that an organisation that exists to ensure fair play in elections should be packed full of ex-MPs and ex-council leaders – jobs for the political boys!”

The Electoral Commission said it has received Banks’ letter and will respond.

Banks said politicians who support remaining in the EU are fuelling claims Russia may have meddled in the referendum and that voters were misled by a widely publicised bus during the campaign emblazoned with a slogan saying Britain was sending 350 million pounds a week to the EU.

The commission previously said it was looking at whether a company called Better for the Country Limited (BFTCL) - of which Banks was a director - was the true source of donations made to campaigners.

BFTCL was not registered as a permitted participant in the referendum but five registered campaigning groups reported receiving donations from it totalling 2.4 million pounds, the Commission said.

Banks, who was pictured with Donald Trump and leading Brexiteer Nigel Farage outside a gilded elevator soon after Trump’s 2016 U.S. presidential election victory, was a registered permitted participant and gave three non-commercial loans to Leave.EU, totalling 6 million pounds.

The Commission said in April it was investigating Leave.EU’s funding as well as looking at whether its spending return was complete.

The Commission has the power to impose fines and other sanctions if it finds rules were broken.