Its claims come as the total number of construction worker deaths continues to rise. Ucatt said last year saw a 25 per cent increase in the number of fatalities, while the HSE said this year a further ten to 15 per cent rise was possible.
Ucatt general secretary Alan Ritchie said that the HSE's falling conviction figures were "profoundly shocking".
"The HSE are clearly failing to follow their own rules and guidelines on prosecutions. Serious questions must be asked about why the HSE is so spectacularly failing to prosecute more companies," he said.
But responding to the report, the HSE suggested that some of the statistics contained in the report were "inaccurate".
Its chief executive, Geoffrey Podger, said that prosecutions were not always possible and that Britain was not a "police state".
"We do not prosecute without proper justification - both evidential and public interest," he explained.
"This issue is in danger of becoming a distraction from the real issue, which is that construction deaths are creeping up again. The question should be 'how are we all going to work together to stop this?'"
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