But even before her death, there were already widespread complaints about the nature of the campaign: that it has not focused on the real issues, has not presented voters with the facts, and has become a series of negative and hysterical claims and counter-claims, leaving voters bewildered and ignorant.
Those arguing for Britain to stay in the EU have focused, pretty unremittingly, on the economy, and the potential risk to British voters of an exit (a "Brexit").
An example of how important this could be was shown by a polling experiment
early in the campaign that asked people how they would vote if they knew they would be better or worse off as a result of Brexit. The question posed -- how much money did it cost to make a difference? £25, or less than $50. That's not per week or per month. That's per year.
In other words, you could alter the outcome of the referendum for less than a dollar a week.
Indeed, at a time when the "Remain" camp had a decent -- if not massive -- lead in more conventional opinion polls, you could produce a clear majority for "Leave" support just by telling people that they would be no worse off outside the EU.
The "Leave" camp, by contrast, has focused on the amount of money the UK pays into the EU. Their claim that this amounts to £350 million ($502 million) per week is much disputed. But in order to challenge it the "Remain" side have to mention it -- which just gives it more publicity -- and even if the debate then focuses solely on the net contribution to the EU, which is around £140 million ($201 million) per week, that still sounds like an awful lot of money to most people.
The other main focus for "Leave" campaigning, though, has been on immigration. They know that it is -- and has now been for years -- the number one political issue in Britain. And they can (fairly) link a lack of control over immigration levels
with EU membership since freedom of movement is a fundamental EU principle, and (less fairly) with the potential future expansion of the EU to include countries such as Turkey
Exchanges over these issues have led to charges of scaremongering and deception, as well as about the character of the individuals involved.
The referendum is not for the most part being debated as a difference of opinion between people who may, genuinely and sincerely, take different views on the issue, but rather as a clash between members of an out-of-touch elite who don't understand the concerns of real people on one side and swivel-eyed racists and liars on the other.
Perceptions of who has been negative largely depend on how one intends to vote
. Pro-Brexiters think that the "Remain" camp has been negative and untrustworthy. Remain think the same of the pro-Brexit arguments.
And it's not led to a terribly well-informed public
either -- although you'd find relatively similar levels of ignorance in almost every election or referendum, anywhere in the world. A belief in the idea-type voter -- someone who gathers in all the information, cogitates at length, then votes in an informed reasoned way -- is a belief only held by people who have never met many voters.
It is, though, not entirely clear why anyone should be surprised by this. It is not the job of election or referendum campaigns to carry out civic education, any more than it is to help old ladies across the road. It's to win. Not at any costs, of course, and the death of Jo Cox has led to some discussion about the nature of political discourse and whether it should be less brutal and more respectful.
But whilst everyone calls for "positive" campaigning, the referendum has also been a useful reminder of the old maxim that positive campaigning is often relatively fact-free campaigning.
Perhaps the most positive campaigning has been "the better world" regularly promised by the Brexit camp, in which Britain has a better economy, lower immigration (but with no labor shortages), lower taxes, and a better funded health service, and so on. Its opponents argue that this is a fantasy, and a con trick, designed to mislead.
But you can't say it's not positive, and, judging from recent polls, it has convinced many people.
Editor's note: Philip Cowley is professor of politics at Queen Mary University of London; he is the author of "The British General Election of 2015," and his next book, "More Sex Lies and the Ballot Box
" is out in September. He tweets at @philipjcowley. The views expressed are his own.