The UK's influence in the world is declining1 and there are now many larger and more powerful countries engaged in debating world politics, setting international norms and facilitating trade deals, for mutual benefit. As a member of the EU, our influence in world politics is massively increased1. The downside is that on some issues the EU moves in directions we don't like, but, this is worth it for the added clout we get in general. On this basis the ProEuropa website lists increased Influence in the World as one of the main reasons why the UK should stay in the EU2, and by early 2013 British Prime Minister David Cameron "acknowledged publicly what Barack Obama has been telling him privately - that retreat from the Union would diminish Britain's influence in Washington, Beijing, Delhi and beyond"3. The USA's administration under president Barak Obama went public with their concerns in 2013 Jan: if the UK left the EU we could end up on a "on a path to international isolation and even irrelevance"4.
In order to gain the benefits of EU solidarity, we must accept that multinationalism should often trump individual national interests. When the EU acts together as a whole, the advantage to all of its members is greater than if countries maintained their own unilateral policies. This enhanced power, gained through solidarity, effects not only trade negotiations, but also boosts international political manouvering and enhances informal influences. The downside is that in some areas, national interests must be allowed to be subsumed into the greater effort. This is like any collection of humans: if you group together, the whole group has more capability, even though individual wishes are sometimes circumvented. Anyway, needless to say that at present the EU is only united on a few, mostly economic, points. Great rewards can be gained in the future if further choices are made at a EU level rather than a national one, especially in energy and foreign policy. The Economist ran an article on this in 2008 with regards to Russian antagonism:
“The European Union will be heeded by Russia only when it speaks with one voice. That was the universal battle cry in Brussels as EU officials and diplomats hurried back from their summer holidays to prepare for an emergency EU summit on the Georgian crises, called by the current French presidency for September 1st. And faced with the sobering sight of tanks trundling around Europe's backyard, there was equally loud agreement among national politicians that their usual squabbling over the right attitude towards Russia harms the common interests of the 27-member union. [...]
A November 'power audit' by the European Council on Foreign Relations (ECFR), a think-tank, argued that Europe was throwing away what should be its considerable leverage over Russia. After all, the EU's population is more than three times that of Russia, and its wealth more than a dozen times greater. The EU depends heavily on Russian energy, but the flip-side is that it is Russia's biggest market for gas (indeed, for all Russian exports). If the 27 EU countries dealt with Russia as one, they would surely have less to fear from Moscow hawks.”
Chatham House, the Royal Institute of International Affairs, is a London-based think-tank, states the following in the conclusion to its research paper on the UK influence in the world:
“For a mid-sized country like the UK, which will never again be economically dominant either globally or regionally, and whose diplomatic and military resources are declining in relative terms, being a major player in a strong regional institution can offer a critical lever for international influence. In the UK's case, this means committing to be a leading member of the world´s principal civilian power, the European Union. [...]
Britain is likely to be richer, safer and more influential in the coming decades if it treats Europe as the `inner circle´ of its foreign and security policy, as well as of its international economic policy. Despite the UK´s many attributes as an international hub, it is wrong to think that it can act alone as a flexible intermediary in an increasingly competitive and networked world; to try to do so would yield ever-diminishing returns.”
Chatham House (2015)
The report also notes that as the UK is a relatively big member, that within the EU we also wield quite a lot of influence as a member state. This influence would disappear almost completely if we were to leave it, meaning, we would still have to comply with their trade laws in order to trade with them, but we'd have no say on how those laws work.