I don't think there is a mechanism for invalidating general election results. The parliament can vote to hold new general elections. For the Brexit referendum,

I don't think there is a mechanism for invalidating general election results. The parliament can vote to hold new general elections. For the Brexit referendum, there is no need to invalidate it, as it was an advisory opinion poll rather than a binding public vote for the government. The UK government could ignore the results or call for a new referendum if they wished to.