A Leveson-style public inquiry is needed into the blacklisting of construction workers – including cases in Scotland – a trade union warned.

Unite described the issue as a national scandal as MPs prepare to debate the issue today.

Yesterday Scottish MPs heard from a senior executive at construction firm Sir Robert McAlpine.

Cullum McAlpine insisted his firm had never operated a blacklist. But he told the Scottish Affairs Committee his company had been a member of the Consulting Association, which unions say held secret files on thousands of workers.

Mr McAlpine said the association had been set up in part to compile a list of those involved in unlawful acts. He said he considered a blacklist to be a list barring someone from working on a construction site. The Consulting Association list had not worked that way, he told MPs, adding that some people should never have been on the list.

These included a disabled war veteran from Dundee, whom Jim McGovern MP said had been listed after the city recognised Nelson Mandela, a move that saw him being seen as a "lefty".

Unite general secretary Len McCluskey said: "This is a scandal on the scale of phone-hacking, except it is the lives of thousands of ordinary workers that have been ruined. There should be a full inquiry.

"Families have been torn apart just because workers raised safety concerns or because they belonged to a trade union."