The United Kingdom and France signed the Northwood Declaration in London on 10 July, committing for the first time to coordinate the use of their independent nuclear deterrents and to mount a joint response to any “extreme threat” to Europe. Prime Minister Keir Starmer called the accord “historic,” while President Emmanuel Macron said a new oversight committee will supervise cooperation across strategy, capabilities and operations. Although each arsenal remains under national control, the declaration envisages shared early-warning data, joint exercises and aligned messaging—steps intended to reassure European allies amid Russia’s war in Ukraine and uncertainty over long-term U.S. security guarantees. France maintains about 290 nuclear warheads and spends roughly €5.6 billion a year on the force; Britain is estimated to field around 225 warheads. The nuclear pact coincides with a decision by French Armed Forces Minister Sébastien Lecornu to restart production of the Franco-British Storm Shadow/SCALP air-launched cruise missile at MBDA in 2025, ending a 15-year hiatus. Paris has placed a fresh order and London is expected to follow, aiming to replenish stocks depleted by transfers to Ukraine. Together with the 2010 Lancaster House agreements, the Northwood Declaration deepens Franco-British defence integration and underscores both countries’ intent to serve as Europe’s nuclear backstop while modernising conventional weapons supplies.