Russian interference with the Brexit referendum was widely suspected, with some relevant evidence, but again the people in charge of investigating and the main suspects had a lot of overlap.
A report was eventually produced saying essentially that the government hadn't done anything to stop Russian interference and didn't seem to care about it. The PM then prevented that report from being published for a long time.
https://en.wikipedia.org/wiki/Russian_interference_in_the_2016_Brexit_referendum