The Great Exhibition

One year's leeway either way. Either 1850 or 1852 was accepted as a correct answer.

Is it just me that thinks one year either way is miserly leeway for something that happened 166 years ago?

You could argue that the Festival of Britain was held in 1951 to celebrate the centenary, but if you're relying on people knowing that, it would surely be better to ask in what year the Festival of Britain was held.

I would have preferred to see (say) ten years either way.