Shadow Chancellor John McDonnell called Winston Churchill "bad guy", provoking Boris Johnson's furious reprimand.
The Labor heavyweight commented on the manner in which Mr. Churchill treated the striking German miners while he was secretary at home in 1910.
Churchill's decision to send troops to help police crack down on riots in Tonypandy has long been the subject of historical debate.
During a question-and-answer session on the Politico website, Mr. McDonnell was asked about "Winston Churchill, hero or villain?"
The Chancellor of the Shadow said: "Tonypandy – naughty."
Mr. Churchill ordered 200 police officers from the Metropolitan Police to enter Tonypandy, with a detachment of Lancashire Fusiliers in reserve at Cardiff.
The soldiers were eventually called to the Rhondda Valley village to help them cope with the situation.
The warlord, who was later knighted, was voted Britain's biggest in a 2002 BBC poll.
Former Foreign Minister Johnson, who has written extensively on Churchill, said McDonnell should be "ashamed" of what he said.
"Winston Churchill has saved this country and all of Europe from a fascist and barbaric racist tyranny and our debt to him is incalculable," he tweeted.
"If John McDonnell had any knowledge of history, he would be aware of the fact that Churchill also had an extraordinary record as a social reformer, who cared deeply about the workers and their lives.
"JM should be ashamed of his words and remove them immediately."
<div data-embed-data = "
If John McDonnell had any knowledge of history, he would be aware that Churchill also had an extraordinary record as a social reformer, who cared deeply about the workers and their lives. JM should be ashamed of what he said and remove them immediately 2/2
– Boris Johnson (@BorisJohnson) February 14, 2019
"data-on-all-screens =" true ">
Sorry, this content is not available on your device.