Justice Secretary David Lammy has condemned the leaking of details from a closed National Security Council meeting on the UK’s response to the escalating conflict involving the US, Israel and Iran, describing the disclosure as an “absolute travesty”.

Lammy’s comments came after reports that discussions from the classified session emerged in the media, including claims of cabinet-level disagreement over whether the UK should permit US forces to use British bases in support of strikes on Iranian missile sites. The Guardian, which first reported the details, said ministers raised concerns about both escalation risks and the legal basis for any involvement that could be viewed as offensive action.

Speaking on Friday, Lammy said the government treated national security deliberations with the utmost seriousness and indicated there would be a push to establish how the information entered the public domain. He said the leaking of sensitive discussions undermined the confidentiality required for the government to take decisions in a rapidly moving crisis.

At the same time, Lammy sought to present a united front on policy, insisting the cabinet remained aligned in opposing offensive military action against Iran. He said the government’s position was focused on protecting UK interests and UK people in the region, and supporting defensive measures intended to reduce the threat from missiles and drones.

The leak has landed at a politically sensitive moment for the government, with the conflict in the Gulf widening since coordinated US and Israeli strikes began on 28 February. Iran has responded with missile and drone attacks across the region, including against military infrastructure associated with the United States and its allies. A number of Gulf states hosting US forces have reported being targeted, as the confrontation has spread beyond initial strike locations.

The UK has insisted it is not a participant in offensive operations, but has faced increasing scrutiny over the extent to which it is providing practical support to Washington. The Guardian has reported that ministers debated whether allowing US aircraft to operate from UK facilities could draw Britain into the conflict as a co-belligerent, even if the activity is framed as defensive.

In recent days, government messaging has drawn a distinction between what it calls offensive strikes and actions described as necessary to prevent further attacks in the region. British authorisation for the use of UK bases, as publicly presented, has been described in terms of limited and defensive support, with the stated aim of reducing the capability of Iranian forces to launch attacks that could endanger UK personnel, assets and shipping routes.

However, the leak has exposed the degree of internal sensitivity about that framing. Critics of expanded support for US operations argue that striking missile-related infrastructure inside Iran may be difficult to characterise as purely defensive, while supporters of closer alignment with the US position contend that disabling launch capability is part of preventing imminent or continuing attacks on allied forces and regional partners.

According to the Guardian, the NSC discussion included disagreements within cabinet, with Energy Secretary Ed Miliband reported to be among ministers urging caution about permitting US use of British bases. The report suggested some ministers were concerned about the consequences of escalation, and about whether the legal justification for UK involvement was sufficiently robust.

Lammy, asked about the cabinet’s stance, said ministers were united in their opposition to an offensive war and said the government’s priority remained the safety of UK nationals and the defence of British interests. He also emphasised the seriousness of the leak itself, portraying it as damaging to the way government must operate during a national security emergency.

The National Security Council is the UK’s most senior forum for decisions on foreign policy and security, bringing together key ministers and security officials. Its proceedings are typically treated as highly confidential, and unauthorised disclosure can prompt formal inquiries and potential disciplinary or legal consequences, depending on the circumstances.

The political fallout is likely to intensify calls for greater transparency and parliamentary oversight as the conflict continues. MPs from across parties have previously pressed governments to set out the legal basis for military involvement overseas, particularly where the UK could be seen to be enabling or facilitating the use of force. Pressure may also build for ministers to provide fuller detail on the scope of any permissions granted to US forces operating from UK-linked facilities, and on the safeguards intended to prevent Britain being drawn deeper into hostilities.

The leak also risks sharpening divisions within Labour as the government balances commitments to the UK-US defence relationship against concerns among some MPs and party members about the legality and wisdom of military action in the region. At the same time, the government faces attack lines from opponents who may argue that public evidence of internal disagreement projects weakness at a time of heightened international risk.

Downing Street has repeatedly stressed that the UK’s actions are aimed at protecting regional stability and safeguarding British personnel, while urging restraint and de-escalation. The situation on the ground remains volatile, with ongoing exchanges of fire and continuing fears of disruption to critical shipping lanes and energy supplies if the conflict expands further.

For now, Lammy’s intervention has turned attention to the immediate question of who leaked details of the NSC deliberations, and whether the breach will lead to a formal investigation, while leaving the underlying policy dispute — how far the UK should go in supporting US military operations linked to strikes inside Iran — at the centre of an intensifying political and security debate.