Image copyright Reuters Image caption Illegal immigrants gather at a border crossing into Europe

A darkening cloud looms over mainstream European politicians in the early months of 2015.

It is the rise of parties and movements seen by them as either extreme or nationalist, sometimes both.

That these relative newcomers have become major players in national politics is viewed not only as a dangerous departure from the natural political order but also a serious threat to the territorial integrity of the state.

Each country in Europe has got its own specific features that contribute to the rise in support of parties other than the traditionally dominant ones.

Mainstream parties have been cautious in addressing concerns about issues like immigration

A common factor, however, is the ease with which capital and labour move from one country to another in the 21st Century.

In the days of strict exchange controls, national governments had greater autonomy in making economic policy making.

Before accepting the freedom of movement which European Union membership entails, governments also had greater control over immigration.

Three I's

Important aspects of the rise of parties deemed (sometimes rightly) to be extremist or nationalist can be summarised as the three i's: inequality, immigration, identity.

Image copyright EPA Image caption Germany has seen a rise in support of anti-immigrant parties

Image copyright Getty Images Image caption Greece's massive debt crisis has led to mounting poverty across the country

The enormous increase in inequality of income over the past generation, plus immigration levels on a scale not hitherto seen in Europe, have contributed to shifting political identities.

The power of supra-national institutions, companies' ability to move plant and offices to cheaper labour markets, and investors' freedom to move their money around have put limits on the powers of national governments, with no country enjoying absolute political and economic sovereignty.

Yet the mainstream parties have, at least until very recently, been somewhat supine in their easy acceptance of the new economic order.

They have been very cautious in addressing the widespread concerns within their societies about extremes of inequality (exacerbated by transnational tax avoidance) and the levels and concentration of immigration.

The expectations of voters may at times have been unrealistic.

Yet, centre-left parties might have been expected, for example, to have opposed far more vigorously central aspects of the transatlantic trade and investment partnership (TTIP), currently being negotiated, which raises the prospect of US companies taking legal action against national governments in Europe.

This would be a further serious blow to the prospect of democratic control over economic policy, putting transnational corporate interests above the public interest, as interpreted by elected European governments.

Greece

There comes a point at which people revolt.

While Greek politics over the post-war era have not been a success story (with the failure of successive governments to collect enough taxes a major part of the problem), the austerity measures imposed on Greece by the European Commission, the European Central Bank and the International Monetary Fund, have accelerated unemployment and further lowered the tax base.

Greece by numbers:

Average wage is €600 (£450: $690) a month

Unemployment is at 25%, youth unemployment is almost 50%

Economy has shrunk by 25% since the start of the eurozone crisis

Country's debt is 175% of GDP

The collective impact has led a disillusioned electorate to sweep Syriza, a coalition of radical left-wing groups with some right-wing allies, to power.

If the present Greek government fails in its attempts to postpone debt repayment, to obtain some debt relief, and to reinvest in their economy and public services, dissatisfaction with them could lead to Greeks returning to the traditional parties.

It could lead to a total disillusionment with democracy itself, in the country which gave birth to the concept.

Image copyright Pablo Blazquez Dominguez Image caption Podemos, lead by Pablio Iglesias, is seen as the Spanish equivalent to Syriza

Spain

Post-Franco Spain has, in terms of the establishment and consolidation of democracy, been one of the world's most outstanding examples of successful transition from authoritarian rule.

Economically, however, it has been a sadder story in recent years. Although unemployment is not as high in Spain as in Greece, it is grim enough - about a quarter of the workforce without a job.

This has led to the rapid rise in popularity (and membership) of Spain's anti-establishment left-wing party, Podemos, the Spanish equivalent of Syriza. It has also made more salient the politics of national (or sub-national) identity.

In Catalonia, demands for more autonomy have increasingly become calls for independent statehood.

Whereas in the UK, the referendum on Scottish independence was granted full legitimacy by the British as well as by the Scottish government, last year's referendum on independence in Catalonia was dismissed as irrelevant and illegitimate by the Madrid government.

Although only about 40% of the population of Catalonia voted, four out of five of those who did opted for independence.

Arguably, the intransigent policy of the present Spanish government has pushed numerous Catalans who were ready to settle for further devolution of power into an embrace of separatism.

Image copyright AP Image caption Marine Le Pen was a candidate in France's 2012 presidential election

France

In a number of European countries, immigration has become a hugely sensitive issue.

It is one which the mainstream parties handle with understandable care, both to avoid inflaming inter-ethnic tensions and because their powers to stem immigration are limited by the provisions of the EU.

The level of immigration has not only been widely regarded as too high (as opinion surveys have shown), it has also led to the rise of nationalist parties with hostility to immigrants being part of their appeal.

Cases in point are three of Europe's most populous and powerful states - France, Germany and the UK.

The strength of right-wing populism has been particularly marked in France where Marine Le Pen's National Front is a serious contender for political office.

In a very recent by-election in eastern France, the National Front were ahead both of the Socialist Party and of the conservative UMP in the first round.

After the UMP, as the third party, was eliminated, the National Front won almost 49% of the votes in the run-off, losing narrowly to the Socialists.

Image copyright AP Image caption Germany's past acts as a counter to the rise of the far right

Germany

In Germany, the strength of the economy, as well as revulsion against the Nazi past, has helped to keep in check the rise of the far right.

Nevertheless, there has been a growth in support for the right-wing virulently anti-immigrant National Democratic Party.

However, this is not on a scale to even come close to threatening the dominance of the Christian Democrats, with their popular leader Chancellor Angela Merkel, and the main opposition party, the Social Democrats.

United Kingdom

In Britain, some of the same issues have led to rapidly shifting political identities.

Parties that could be dubbed neo-fascist, such as the British National Party, have made little headway. UKIP, however, has made great strides.

In the last few years, it has gained a strong representation in the European parliament, a continuing rise in opinion polls, and two defectors from the Conservative Party who have gone on to win the by-elections triggered by their moves.

UKIP's responsiveness to concerns about levels of immigration is a major part of their appeal in England.

The Scottish dimension

Against expectations on the day of the Scottish referendum in September 2014, the Scottish National Party (SNP) now looks as if it could very well be the third largest party in the House of Commons after 7 May 2015.

Image copyright Getty Images Image caption Scots' sense of national identity has led to increased demands for maximal devolution

Opinion polls in recent months have suggested that for the first time, a majority of Scottish seats will be held by the SNP.

That would be a massive switch of allegiance, reflecting the fact that fewer Scots than in the past feel both British and Scottish.

It is also, however, strongly related to the disparate outcomes of UK-wide and Scottish elections, whereby the Conservative Party won just one seat in Scotland in 2010 but did well enough in England to become the dominant partner in a coalition government.

Given Scots' centuries-old sense of national identity, this has led to demands for maximal devolution of power, with increasing numbers calling for separate statehood. The party has fostered and channelled this sentiment, albeit while espousing a civic rather than ethnic nationalism.

The SNP has little in common with UKIP, still less with Le Pen's NF. They are pro-EU and open to an increase in immigration and the size of Scotland's population.

Do the new parties have new ideas?

The anti-establishment parties which have made headway in European politics have not, on the whole, come up with radically new ideas.

Those anti-establishment parties which have progressed have done so primarily by responding to strong public dissatisfaction with aspects of the status quo inadequately addressed by the hitherto dominant parties.

Political aspirants who have never held governmental office have the luxury of being able to espouse mutually contradictory and incoherent policies.

Anti-establishment party support after Greek legislative elections

Syriza: 36% or 149 seats in the 300-seat parliament, 25 January 2015, BBC News

Front National: 30%, 29 January 2015, Marianne magazine

Podemos: 24%, 4 February 2015, CIS research centre

United Democratic Party, No polling data available but thought to be less than 5%

Their promises may be attractive, but the sums do not add up.

Experience of government leads to necessary compromises and modification of policies concocted when office appeared a distant prospect.

Generalisations across Europe come up against important national and local differences.

Yet, a common element is the tension between the power of supranational and often unrepresentative and unaccountable bodies and people's desire to reassert national and democratic control over their own destinies.

Archie Brown is Emeritus Professor of Politics, University of Oxford, and the author (most recently) of The Myth of the Strong Leader: Political Leadership in the Modern Age