BRUSSELS/STRASBOURG (Reuters) - Sweden’s far-right, anti-immigration party will double its seats in the European Union parliament next May if it matches the 17.6 percent it scored in a national vote on Sunday that came as a jolt to Europe from historically liberal Scandinavia.

With four of Sweden’s 21 seats in the 705-member chamber, the Sweden Democrats’ voice would be small. But it will find an echo from many other parts of the European Union, as a Reuters analysis of recent national ballots and opinion polls suggests a euroskeptic bloc may grow by some 60 percent in the Parliament.

That would leave those who are hostile to deeper EU integration with around a fifth of the legislature, not enough to push any big changes but enough to challenge the established parties and crack open internal divisions soon after Britain leaves the bloc next March.

The Reuters analysis is based on the latest available polls by reputable agencies in the EU’s 27 remaining states, or actual national election results in those countries which have held an election more recently than the last poll. Most of the polls ask people how they would vote in a hypothetical national election. Most countries use proportional representation in EU elections, making translating vote share into seats relatively simple. Voting by regions in Italy and Ireland where opinion polls offer only national data complicates that process and so the seat count analysis makes some further assumptions.

While aggregating different polls is non-scientific and provides little more than a snapshot, it is a method used by some EU officials internally - including at the EU assembly itself - to get a sense of the shape of the next parliament.

The latest data indicate a clear strengthening for movements beyond the mainstream at a time in which Steve Bannon, an architect of President Donald Trump’s election win in the United States, has launched a project to push the anti-EU vote across the Union.

The current popularity of the anti-establishment parties in Italy’s new coalition, 5-Star and The League, boosts the possibility their current blocs in Brussels will increase in strength. Their ratings, and the rise of Alternative for Germany, more than offset the loss to the anti-EU camp of the UK Independence Party, whose 19 members will leave along with Britain, leaving a smaller chamber.

Polls suggest the EFDD grouping, dominated today by UKIP and 5-Star, could grow to 58 from 45 seats if alignments are unchanged. The ENF grouping, which includes Marine Le Pen’s French National Rally and Geert Wilders’ Dutch Freedom Party, could nearly double to 62 seats from 35, thanks in part to the surge in popularity of The League in Italy.

That would take the two right-wing groupings’ combined total to 119 seats from 78 and their share to 16.9 percent from 10.4 percent, as the total number of seats falls to 705 from 751.

SHIFTING ALLIANCES

That analysis assumes the eight transnational party groupings in the current chamber will stay the same. In reality, new alignments in the next EU legislature will depend heavily on horse-trading and switching loyalties. Italy’s 5-Star has previously explored joining the pro-EU centrists in Brussels.

Other parties could shift to more overtly euroskeptic positions. These might include members of the ECR, set up by Britain’s ruling Conservatives as a euroskeptic alternative to the main center-right EPP and which will now lose British seats.

Poland’s ruling Law and Justice Party could seek a new home outside the ECR. But like Hungarian Prime Minister Viktor Orban whose Fidesz party is a controversial member of the EPP, they do not share some hardliners’ goal of breaking up the EU altogether – not least because Brussels gives them substantial subsidies.

Elsewhere on the political spectrum, the collapse in elections last year of the traditional left and right in France suggests a potential boost for the European Parliament’s centrist bloc ALDE – should President Emmanuel Macron’s new movement aligns with it -- and for the somewhat loose alliance on the far left known in Brussels as GUE.

The polling analysis suggests the EPP, including German Chancellor Angela Merkel’s Christian Democrats, would remain the biggest group. It would shrink to 186 seats from 219 in the smaller chamber but hold its lead over the center-left S&D.