"Statistically, it is insignificant, given the population size..."
Please show your workings and assumptions.
By my reckoning 1.2m is just shy of 2% (1.83%) of the population in 2016 (65.64m from websearch)
So I would say that was significant at the 1% level (P>0.01).
If you take it on the population who voted it rises to closer to 4%.
Ok my back of a fag packet analysis may be wrong - but at least there is some analysis to support my argument.