BBC's 1957 Spaghetti Harvest prank

The Spaghetti Tree prank (wiki) from the April 1, 1957 episode of the BBC Program Panorama:

Here's the explanation:

On April 1, 1957 the British television programme Panorama broadcast a three-minute segment about a bumper spaghetti harvest in southern Switzerland. The success of the crop was attributed both to an unusually mild winter and to the virtual disappearance of the spaghetti weevil. The audience heard Richard Dimbleby, the shows highly respected anchor, discussing the details of the spaghetti crop as they watched video footage of a Swiss family pulling pasta off spaghetti trees and placing it into baskets. The segment concluded with the assurance that, For those who love this dish, theres nothing like real, home-grown spaghetti.

The Swiss Spaghetti Harvest hoax generated an enormous response. Hundreds of people phoned the BBC wanting to know how they could grow their own spaghetti tree. To this query the BBC diplomatically replied, Place a sprig of spaghetti in a tin of tomato sauce and hope for the best. 

To this day the Panorama broadcast remains one of the most famous and popular April Fools Day hoaxes of all time. It is also believed to be the first time the medium of television was used to stage an April Fools Day hoax.

Since 1955 Panorama had been anchored by Richard Dimbleby, whose authoritative, commanding presence had made him one of the most revered public figures in Britain. If Dimbleby said it, people trusted that it was true. Which is one of the reasons why the spaghetti harvest hoax fooled so many viewers. His participation lent the hoax an air of unimpeachable authority.

Almost no one else at the BBC knew about it. The segment was not mentioned at all in the pre-transmission publicity handouts.

The line-up for that days show included a long segment about Archbishop Makarios, leader of the Greek Cypriots, and a clip of the Duke of Edinburgh attending the premiere of the war film The Yangtse Incident.

The second-to-last segment was about a wine-tasting contest, and then it came time for the spaghetti harvest.

Dimbleby, sitting on the set of Panorama, looked into the camera and without a trace of a smile said: And now from wine to food. We end Panorama tonight with a special report from the Swiss Alps.

The screen cut away to the prepared footage. When it was all over, Dimbleby reappeared and said, Now we say goodnight, on this first day of April. He emphasized the final phrase.

Panorama never attempted another April Fools Day spoof, despite numerous calls for a sequel. However, the hoax did inspire a number of similar stunts in its honour.

This film footage is from the Archive Collection held and administered by the Alexandra Palace Television Society.