Paramedics performed emergency surgery on a 66-year-old man at the scene, but he suffered a cardiac arrest and was pronounced dead.
His brother, who is in his 70s, also suffered chest injuries.
He was airlifted to Frenchay Hospital near Bristol, where he remains (Tuesday).
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The agricultural event is now in its 157th year and although there was heavy rain forecast, it didn't deter the crowds.
In true Bank Holiday style we will see some rain for a time today. However, the rest of the week is looking drier, brighter and warmer.
Big Ben's famous booming bongs will be out of action for several months during urgent repair works, the House of Commons has announced.