Carillion's Midland Metropolitan Hospital construction site is seen after the company went into liquidation, in Smethwick, Britain January 15, 2018. REUTERS/Darren Staples

(Reuters) - Britain’s biggest labour union on Monday called for a criminal investigation into key individuals involved in the collapse of construction and outsourcing company Carillion.

Carillion, which provided services in defence, education, health and transport, collapsed in January, becoming the largest construction bankruptcy in British history. It left creditors and the firm’s pensioners facing steep losses and put thousands of jobs at risk.

The Unite union launched legal action against Carillion in July on behalf of workers who were made redundant. It also called for a public inquiry into the collapse in August.

"There must be an immediate criminal investigation into Carillion ... If no laws were broken, then we need, better, stronger laws," Unite assistant general secretary Gail Cartmail, said here in a statement.

Unite did not name which individuals it wanted investigated, but said it had stepped up its call following revelations “exposing the mismanagement and highly dubious practices which led to Carillion’s collapse”.

Carillion’s chairman Philip Green told lawmakers in February: “My responsibility is full and complete - not necessarily culpability but no question about full responsibility,” when asked about the firm’s collapse.

Green chaired the firm from 2014 until it was put into liquidation after the government refused to bail it out.

Some lawmakers have said Carillion’s collapse shows the risks of using private companies to cut the cost of delivering public services and its failure could be repeated if the government does not learn lessons.