Merlin Attractions Operations Ltd, which acquired the Grade 1* listed castle in 1978, was prosecuted over the death of 72-year-old George Townley, who suffered devastating head wounds in the December 2007 tragedy while exiting the monument.
 
"At about 4.30pm he was leaving via the Bear and Clarence Bridge when he tripped over the parapet wall on his left hand side, fell head first into the moat, and thereby suffered fatal head injuries," Lord Justice Gross told London's Appeal Court.
 
The judge who sentenced Merlin Attractions said that the company had a generally good safety record at the castle, but that its safety failings relating to the Bear and Clarence Bridge represented an "uncharacteristic blind spot which had fatal consequences".
 
The main bridge to the castle has three-feet high stone walls on either side, but the bridge over which Mr Townley came to grief had a 13-inch parapet.
 
The company was convicted of two offences under the 1974 Health and Safety at Work Act at Warwick Crown Court in April this year, and hit with the £350,015 fine.
 
It was also ordered to pay £145,000 in prosecution costs.
 
The case reached the Appeal Court as the company's lawyers challenged the sentence with claims that the punishment was disproportionate to its "generally responsible attitude towards health and safety".
 
But Lord Justice Gross rejected claims that the total fine and costs order was "manifestly excessive" and ruled that it was "within the appropriate range, albeit towards the top end of it".
 
"Notwithstanding the company's generally good health and safety systems, its good record and the other mitigating features...it seems to us that the judge was entitled to conclude that the total fine...had to be measured in hundreds of thousands of pounds," he added.
 
The judge was entitled to conclude there had been a serious breach of the company's health and safety systems and "that that had resulted in an obvious danger of at least serious injury, not so much in relation to adults, but in relation to children, to which a very large number of people had been exposed over many years".