Why did Burnham retract his Russia Brexit interference claims?

Prime Minister Andy Burnham retracted his Russia Brexit interference claims after admitting within 24 hours that he had no evidence to support them [3]. His initial assertion that Russia had interfered in the 2016 referendum triggered a political backlash, including fierce criticism from Boris Johnson and other MPs [3]. The Government subsequently clarified that whilst Russia may have attempted to exploit the vote, it did not succeed in changing the outcome [4].