Clearly the influence of populist politics is no less malign in the UK than in Europe. The issues which exert greatest pressure from the fringes onto the mainstream of British political debate are all fundamentally concerned with Britain's place in the world. UKIP exacerbates the traditional split within the Tory party over Europe, while the SNP, Plaid Cymru and the Greens have effectively issued an ultimatum to Labour over Trident renewal. Trident has no conventional military utility, but is strategically significant in terms of Britain's international position. Its symbolism in electoral terms is as a proxy for the type of international engagement which the various parties desire for Britain. The foreign policy paralysis this has created in Westminster risks Britain drifting into international irrelevance. Philip Hammond sought to downplay Britain's exclusion from Ukrainian negotiations by suggesting that Cameron was instrumental in securing EU sanctions. In reality, this makes the UK's silent acquiescence in the Franco-German pursuit of short term peace in Ukraine at any cost all the more reprehensible.

Across Europe, the impact of populism has been to drive the  mainstream political focus inwards, towards nationalism. The same trend is true in the UK. The SNP exploits the fact that north of the border Trident has become totemic for questions of independence from Westminster. The SNP's trumpeting of the imposition of "foreign" elite rule in Scotland finds its intellectual mirror in UKIP's fusion of the threat to the UK from Europe and immigration.

If Britain truly sees itself as a major player in international politics or at least with its European neighbours, her failure to engage is contributing to the undermining of the normative contours of Europe. The twin challenges of populism and Russian autocracy make the nuances of David Cameron's soft Euroscepticism look worryingly like a relic of the 1990s and perhaps a sideshow to  the historic unravelling of Europe.

The direct implications for UK foreign policy of potential coalitions are hard to predict, because populism has had the effect of shaping mainstream political debate and it has placed constraints on government policy. Syriza's victory only exacerbates this trend by putting pressure on Cameron's EU balancing act. His ambiguous approach, on the one hand seeking to placate UKIP and Tory Eurosceptics, while on the other supporting Angela Merkel on EU-Russia sanctions and reform, has left the UK deeply vulnerable, with the imminent prospect of "Grexit". The possibility of cooperative Anglo-German reform of the EU may well be overtaken by revolution from below—a widespread renegotiation by the most indebted eurozone members. By necessity the maintenance of the single currency has become the number one priority for the EU and "Brexit" has slipped further down the agenda.

Syriza's victory should be a source of concern for both main parties. Like many of Europe's populist parties, Syriza maintains ties to Russia, not least because it sees economic recovery tied to maintaining trade links. Although Greece acquiesced in the continuation of sanctions against Russia before the Ukrainian ceasefire, it is unclear how this relationship will play out over time. The Greek Right, with whom Syriza finds itself in coalition, traditionally views Russia as its ally, not least because of their shared Orthodox faith. Greece could act as a Russian Trojan horse, given the unanimity required by EU and Nato decision-making. There is a precedent in former President Andreas Papandreou's balancing act in the 1980s, at first threatening to take Greece out of Nato and the Common Market, only to perform a volte-face once in office. Eurosceptic delight at the blow to the EU is being echoed in the halls of the Kremlin. Emboldened by effective victory in Ukraine, Russia is likely to continue its destabilising support for European populism. Given the implications for European politics, it is striking that neither Cameron nor Ed Miliband has engaged seriously with this issue.