This just in: Stephen Harper has revealed he's a closet Liberal, but will be running for the Green Party in the next election.

O.K., so it's not a very believable April Fool's Day joke, but then the people who occupy the seats on Parliament Hill make fools of themselves all year long - although it's the voters who often feel duped.

Political jokes aside, welcome to the day when pranks are permitted and even expected and you don't have to be a scam artist to put something over on someone.

It's been going on ever since you can remember but where did April Fool's Day start? It's no jest to say that answer has been forever lost to history, but the best guess seems to trace the origins of the daffy day back to France in the 1500s.

That's when the country changed its calendar to the one we follow today, with the year starting in January instead of late March or even April. But with no modern communication methods in those days, word didn't reach smaller communities for years, and many continued to celebrate the New Year in April.

Legend says their lack of enlightenment led them to being called "April fools" and the term stuck.

Or perhaps that history is just an April Fool's joke itself.

Others maintain age old European rites of spring and renewal are the long lost link, with the coming of the new season after the cruel winter a time for joy and pranks.

Whatever the real story - and we'll never know for sure - the day has evolved into the one time of year that normally respectable news media outlets will try to put one over on viewers and readers without apology.

Among the most famous: a BBC report of a huge spaghetti crop harvest in Italy, complete with pictures; a U.S. vote to change the value of pi; the introduction of a left-handed hamburger by a fast food outlet, and a ridiculous story about Taco Bell buying the Liberty Bell for advertising purposes.

Perhaps the most successful of all time in Toronto came in 1977, two years after the federal government chose April 1st as the day the gradually introduced metric system officially transformed our roads and weather forecasts.

Temperatures were already being given in Celsius and cars featuring kilometres as well as miles on their speedometers began turning up on city streets.

And it was because of that unique timing that our sister radio station, CFTR - now known as 680 News, but then the city's biggest rock station - pulled off one of the best media pranks in Toronto history.

The station announced that in addition to all the other changes, the government had hidden the fact that we were also converting all our clocks to metric time. That was followed with a huge explanation of the mathematical machinations behind the new scheme, including that an hour would now be 100 minutes and the 24 hour day would be cut to 10.

Some examples stated 4:15pm would now be 8:24am, while midnight would be observed at 7:05am on the dot.

The station also had an "expert" who explained how it would work and asked people on the street for their reaction, getting some angry with the news their watches and clocks would be rendered useless and others who claimed they'd heard about it being used elsewhere!

The station even started giving the time out in both versions on air, and in the days before the Internet, encouraged confused listeners to call a specially set-up hotline that would explain it all.

People already upset with the changes became furious at the announcement, blaming the government for its stupidity and the phone lines were jammed as listeners called in by the thousands. They were greeted by an elaborate and detailed recording, explaining the new standard and how to convert the old time to the new format.

Those who listened long enough to the spiel finally understood they'd been had, when it ended with an "April Fool's Day" greeting and the hope they weren't too mad.

It was a fabulous idea and execution tied to a once-in-a-lifetime historic change that can likely never be repeated. And it remains one of the best April 1st pranks in local Toronto history.

Hear the exclusive audio of this rare bit of Toronto radio history below. It features morning anchor Bob Holiday, reporters Randall Stevens and Glynnis Bell and a snippet or two from longtime former morning man Jim Brady.

For a look at the top 100 April Fool's scams of all time, as ranked by the Museum of Hoaxes, click here.