Behind the smokescreen of speeches and declarations, the re-elected Conservative government in Britain has set a course that is more likely than not to engineer an exit from the European Union (EU) -- Brexit. In the slipstream, a second referendum in Scotland will break up the union with England. Not very many favor such an outcome, but the momentum will be too strong. Leading politicians are too weak and do not invest political capital to ensure the by far best outcome in the eyes of most people: Britain in Europe and Scotland in the UK.
Prime Minister David Cameron opts for some kind of renegotiation to kill several birds with one stone, and to keep the Tory party united to campaign actively for continued EU-membership. From his point of view that would be wonderful, opening the door to the hall of fame; unfortunately, there is a lot of wishful thinking mixed with flawed analyses embedded in his policy.
The other EU members do not want Britain to leave, but widening or deepening Britain's exceptions goes against the whole idea of European integration: solidarity, common interests, no discrimination based on nationality. If Britain gets a la carte membership, politicians in other member states will be in the mire when confronted with the question, Why not "us"? The next question will be, Why should "we" negotiate in the EU, seeking compromises and consensus, when threatening to leave is apparently the way to get our will? The core of the European idea, the interests of the rest of the EU and their domestic politics cannot be brushed aside just like that.
Concessions may be forthcoming, but steered by the above mentioned political imperatives they will resemble something like the lowest common denominator.
Unless and until they are convinced that the British government musters sufficient support to win a referendum, the other member states, bearing in mind the political costs for themselves, will be reluctant to accommodate Britain. If treaty changes become necessary, ratification in all member states will expose a result to public debate. The more committed the British government is and the more it demonstrates willingness to invest political capital, the more it can get. There is the rub.
Overall conclusion: Unless we are very lucky the world had better brace itself for a self-tortured Britain, not like the country the world had got used to, and for an EU searching for a way forward with less global influence, connoting a lower profile in areas of soft power -- climate change, global trade, human rights, peace keeping operations to name a few examples -- where the member states, through determined efforts, did carve out a respectable role. It may not be fashionable nowadays, but nonetheless this stance may have been helpful to the US by enlarging its room to maneuver. The geopolitical balance may tilt more not only toward instability, but also toward the hard power favored by certain disturbing forces, primarily around EU's borders.