Britain’s biggest tobacco manufacturers have threatened to sue the Government if it introduces plain packaging legislation.

British American Tobacco, JTI and Imperial Tobacco have spoken out against the proposals, which are being voted on this month. They say that they will infringe international law, threaten future investment into Britain and set a dangerous precedent for other sectors.

“If regulation comes through, we will be forced into the position of a legal challenge,” said Jerome Abelman, BAT’s director of corporate and regulatory affairs. “Once the regulations become law, we expect the lawsuits will follow very quickly.”

Daniel Torras, JTI managing director, said the company would challenge the legislation should Government proceed. “Plain packaging would infringe important principles of EU law, and other fundamental rights – including trade mark rights – and goes against obligations under UK and World Trade Organisation rules,” he said.

If passed, the law could come into effect as early as May 2016.

Meanwhile, Ireland has become the first European Union member state to pass a law mandating plain packaging for tobacco products.

The legislation will be sent to the president to pass into law following a technical vote at the start of this month, and the law will be implemented in May 2017.

Deirdre Healy, John Player corporate affairs manager, said the move in Ireland will “deprive us of our intellectual property rights”.

“It is regrettable that Minister Reilly [former Ireland health minister] has stampeded this legislation through in an effort to be ‘first in Europe’ to introduce the measure,” she said. “We are currently considering our legal options.”

Westminster plain packs rally: As it happened.