CONSERVATIVE attempts to effectively ban strikes were dealt a blow yesterday when a United Nations agency confirmed that the plans could break international law.

The Tory manifesto, launched by PM David Cameron on Tuesday, includes a pledge to put a 50 per cent turnout threshold on all strike ballots.

Nurses, teachers and firefighters are among workers facing even bigger barriers under the Tory policy, which would require at least 40 per cent of eligible voters to back action in “essential services.”

But the International Labour Organisation (ILO) has told the Star that the policy could contravene one of its conventions.

Its intervention comes after the Star revealed on Wednesday that international labour lawyer Daniel Blackburn believed the thresholds would be illegal.

The expert explained that they would breach ILO convention 87 on freedom of association and the right to organise.

He told the Star that the ILO “has confirmed that, in strike ballots, only votes that are actually cast can be counted and that the assessment of quorum and majority must be fixed at a reasonable level.”

Asked by the Star to clarify its position, an ILO spokesman said: “We can confirm the position of the ILO committee of experts on the application of standards is as stated (by Mr Blackburn).

“The specifics of the proposal would still need to be assessed within the framework of the appropriate ILO procedures.”

The ILO would investigate the legality of the policy if it was implemented and if a complaint was made by British trade unions, the spokesman for the Geneva-based UN body added.

Mr Blackburn is convinced that a 50 per cent threshold would not be judged “reasonable” by the ILO.

The Star asked the TUC whether it would make representations to the ILO if the Tories were re-elected.

“The general council will urgently consider how to respond to these proposals if the Tories do win the election with a majority that is sufficient to allow them to proceed,” said TUC head of employment rights Sarah Veale.

“As things stand, we remain opposed to all the Tory proposals on strikes.”