Brexit has prompted an urgent and necessary debate on the future British relationship with the European mainland. It has recently brought to mind the observations made by William Gladstone following the Prussian defeat of France in the late 19th century, wherein he praised relative British detachment from the continent and warned against our potential abstention or acquiescence. “I cannot help but feel that we have some reason to be thankful,” he argued, “but I admit, and am the first to admit that, whatever be that security, power, and independence, we have no right to wrap ourselves up in an absolute and selfish isolation.” Isolationism has been a longstanding vice in British strategic thinking. Until the end of the Second World War, the UK flip-flopped between international engagement and withdrawal, not least in relation to its own neighbourhood. When the continent was in broad equilibrium, Britain withdrew to cultivate its imperial concerns, though when the balance was pulled out of alignment by a European irredentist or revisionist, the country thrust its power behind a coalition to knock the power grabber down. One thing the UK has maintained for the past two centuries is robust Armed Forces, always in the form of the Royal Navy – critical for an island power – and when needed, a potent Army and Air Force. Today, however, with NATO reporting that the British defence budget is one of the lowest in history (as a percentage of national income), the Ministry of Defence faces another spending crisis and key capabilities are said to be on the line. These include the Royal Navy’s amphibious capability, in the form of the significant numbers of marines and the Albion class assault vessels. As it withdraws from the European Union, and as the Government undertakes a reappraisal of the 2015 Strategic Defence and Security Review, it is wholly inadvisable for further reductions to be made to the British Armed Forces. Aside from the fact that it would stoke further allegations of Britain’s global decline, the nation is increasingly confronted by another momentous chapter of geopolitical flux. The rise of Chinese power and the resulting uncertainties visited on Europe by the administration of President Trump; the geopolitical irredentism and revisionism of Russia; the export of Islamist extremism from the Middle East; and changing dynamics within the continent’s own political architecture all have the potential to spill over and explode. A new report by the Henry Jackson Society – ‘Global Britain’ and the Future of the Armed Forces – argues that, unless the link between UK military capabilities and interests is realigned, it will become increasingly difficult to confront the new challenges or embrace the new opportunities as the country withdraws from the EU. Thus, over the next five years, we believe that London should allocate an additional 0.2% of national income to the British Armed Forces until a military budget equivalent to 3% of GDP is achieved. This would be around the average (3.2% of GDP) of British expenditure over the past 40-year period (1978-2017). In terms of hard currency, this means defence spending would reach approximately £71 billion (current prices) by 2022. Since the European neighbourhood is the one which Britain can truly call its own, 2% of GDP should be spent to provide military capabilities for NATO, including nuclear forces. An additional 1% of GDP should be allotted to underpin British interests beyond Europe, particularly to secure new commercial partnerships in the rising Indo-Pacific zone, a volatile region whose countries may request British military input in exchange for trade agreements. Finally, similarly to the International Development Act 2015, guaranteeing the Department for International Development a yearly budget of 0.7% of GDP, an Act of Parliament should be passed to mandate the defence spending baseline (i.e. 3% of GDP), providing the Ministry of Defence and the Armed Forces with greater continuity when undertaking defence planning. As the deadline for leaving the EU looms closer, Britain cannot simply rely on the mantra that ‘Brexit means Brexit’. London ought to provide the resources to generate the capabilities to match its vision of life after withdrawal. This means taking necessary precautions to safeguard Britain’s core national interests through the incremental expansion of the defence budget. All this will prove meaningless, though, if the UK fails to effectively combat the reactionary strain of isolationism that – as Gladstone himself elaborated – would make us “unworthy of the recollections of our past, unworthy of our hopes of the future, [and] unworthy of the greatness of the present.” Put another way, future generations will measure the success of Brexit against the government’s political capacity to ensure that the UK continues to punch above its weight. Written by James Rogers with Jack Wright, who is Senior Research Assistant for the Henry Jackson Society’s Global Britain programme.