BNP, EDL, Britain First account for what proportion of electorate? 1%? Less than 1%? of course the Leave campaign suits them, they are very right wing to a point of extreme, however they are not representative of the electorate. They are almost as right wing as the government that France nearly got earlier this month - now that's scary. Just to put this in perspective, at the last general election the Monster Raving Looney party got more votes than the BNP by quite a margin. I don't see them on your list.
The SNP received fewer votes than UKIP in the last general election, in fact even the Liberal democrats got more votes than the SNP, the SNP are a minorty party with 4.7% of the votes on a national level. Sinn Fein received 0.6% of the votes cast in total.
Actual results here:-
Results of the 2015 General Election - Election 2015 - BBC News
So to suggest any of the parties above represent the voting electorate shows you clearly don't understand some fundamentals.
Meanwhile, the leader of the Labour party, who spent most of his 40 year career campaigning against the EU as a Eurosceptic is now leading the Labour In campaign. Asked last week on TV on a scale of 1-10 where would he say he was with regard to the UK staying in the EU replied - seven to seven and a half. That's confidence for you.
Julian put this entire referendum in perspective a few posts back.
The entire referendum is about Control and Choice. We are voting to control and choose ourselves or hand over the power to a third party government of officials we have not chosen. It really is that simple.
You can then apply that argument to immigration, business, finance, tax, racism etc etc, but it doesn't change the fact the vote is about nothing more than control and choice.