RMT report finds that between 2006 and 2022, the train operating companies invested just 1% of the money spent on the railways.
Train company bosses take little risk with their capital but have benefited from profits before tax, of 126% of the capital invested by rail operators.
65% of profits are locked away in shareholder dividends instead of being redistributed into improving the railway or upping workers wages and improving conditions.
The report comes on the day of the latest strike action by 20,000 railway workers in a long running dispute on pay jobs and working conditions.
RMT general secretary Mick Lynch said: “Train companies invest little or nothing in our railways and make completely unjustifiable profits which they squirrel away in shareholder dividends and bosses pay packets.
"It is a scandal that the travelling public is being ripped off by greedy rail privateers while at the same time the government oversees a corrupt system and prolongs a rail dispute for political reasons.
"It is high time this profits bonanza gravy train was halted, a deal done with the RMT and the railways returned to public ownership for the good of the country and railway workers."