The “corrupt and illegal practices” of the Vote Leave campaign in the 2016 referendum undermine the validity of the decision to leave the EU, the high court has been told.

Relying on findings made by the Electoral Commission about overspending by the pro-Brexit campaign, British people living in Europe have launched a legal case arguing the referendum result should in effect be set aside.

“Breaches of spending rules are serious offences that vitiate the referendum result,” Jessica Simor QC, for the claimants, told the court. “Corruption and illegality in the course of an election or referendum must have a consequence. Corruption and illegal practices undermine the rule of law and democracy.”

There was significant overspending, data breaches and possibly Russian involvement in the referendum, she said. “The electorate can no longer be expected to respect the result.”

See full story in The Guardian