Once you’ve watched Brexit: The Uncivil War, starring Benedict Cumberbatch, you may never enter a Facebook ad contest again.

In the movie, based loosely on real events around Brexit, Facebook ads are an important tool in the hands of the dark artists who helped cyber-engineer the referendum victory for the Leave side in Britain’s 2016 referendum on the European Union.

Cumberbatch plays the part of Leave campaign director Dominic Cummings — in real life, now a chief adviser to British Prime Minister Boris Johnson — who sets up a sophisticated digital campaign to reach disengaged, disgruntled citizens.

One method includes mining personal data from unsuspecting voters using a bogus British-football-themed contest, in which everyone who clicks to enter the contest also hands over their valuable Facebook information to the Leave campaign.

It’s a very good movie for Canadians to watch as we’re about to head into an election campaign.

While the movie is part fiction, anyone who has been following the news over the past few years, especially the scandal over Cambridge Analytica and its role in Brexit and Donald Trump’s victory, will recognize the warning flags raised by the film.

It may not be news that social media can be used for nefarious political purposes in the heat of electoral campaigns, but citizens can’t be reminded often enough that Facebook is a medium that not only sends information to its audience, but gathers it as well.

Facebook, to be fair, has put in place a lot more transparency measures since Brexit and Cambridge Analytica, including an advertising library that allows you to see the who, what, when and how much behind election ads elbowing their way into your Facebook stream.

For instance, when I checked the library on Monday, I learned that the Liberal Party of Canada has spent $242,426 on Facebook ads since June. I could also click on individual ads to see where they were targeted. One, featuring a caption “Let’s build on the progress we’ve made,” was specifically aimed at male Facebook users in Manitoba, British Columbia, Ontario and Alberta and rolled out over the weekend.

The more you look through the library, the more you may be wondering what kind of target voter you are. If you are on Facebook at all — and more than 23 million Canadians are, according to most estimates — chances are you’ve already given some thought to why certain ads are appearing in your newsfeed. I know I have: Facebook’s ad algorithm has some really strange ideas about what I’m interested in buying. (Surprise gift-box subscriptions? Really?)

On Monday, I sat down with Sam Jeffers, co-founder of something called Who Targets Me — whotargets.me — an Internet-based effort to help voters see which political parties are trying to catch their interest on Facebook. Jeffers is based in the U.K., but he’s in Canada this week in hopes of getting voters to sign on while the federal election is under way.

To find out what the political parties like about your Facebook page — or, why you’re suddenly seeing Justin Trudeau, Andrew Scheer or Jagmeet Singh amid posts and photos from family and friends — you attach a Who Targets Me extension to your browser software. Here’s how the Who Targets Me website explains what happens next:

“The software collects the Facebook adverts you see and adds them to the Who Targets Me database. Once you start to see political adverts, it provides you with a personalized breakdown of those posts, along with links to them, and information about why you were targeted with that advert.”

Jeffers said that you’ll be able to learn whether you’ve been targeted because of your age, gender, your geography or maybe even your interests. In turn, you’ll get some valuable hints about where the Canadian political parties believe they need to turn up the charm to get your vote. Basically, it’s the virtual equivalent of yelling at a telemarketer: “How did you get my number?”

The targeted interests could be enlightening. Years ago, for instance, Conservatives told me they’d learned that snowmobile owners were more likely to vote for them, so they specifically aimed their marketing to snowmobile magazines and users. It’s not clear whether Who Targets Me will be able to gather data like that, but I’d be keen to know whether parties are trying to match hobbies or consumption patterns to their voter targets, on top of gender, age and geography.

None of the ad-transparency efforts are going to catch political ads posing as fake-football contests, though, or blatantly fake news stories romping around Facebook. You have to actually pay for an ad to be subject to scrutiny from Facebook or Who Targets Me.

But if you’re looking for some motivation about why to pay more attention to social media in the coming election campaign, watch the Brexit movie.

Susan Delacourt is the Star’s Ottawa bureau chief and a columnist covering national politics.