It may not be the election issue that animates Scottish voters most.

But Europe is certainly the one that has foreign governments and foreign investors most worried.

The rest of the world has a lot invested in the UK being in the European Union - and not just cash.

During last year's referendum even the relatively slim chance of a Scotland not being in the EU immediately after independence gave the jitters to international partners.

But the prospect of a UK-wide vote on a "Brexit" has got the world really nervous.

This week David McAllister, the German Conservative MEP with a Scottish father, dropped usual conventions of political neutrality to urge a "Bremain".

With the US, Japan and other EU members making similar noises, it's clear this issue is not domestic politics as usual.

David Cameron, if re-elected, says he will renegotiate Britain's place in the UK and put the resulting deal to the people.

His current coalition partners, the pro-European Lib Dems, have not made blocking a referendum a red line issue in talks of another concord with the Tories.

Other potential allies for Mr Cameron, Northern Ireland's DUP and the UKIP, also want a vote. That means it may be up to Labour and the SNP to forge an alliance to stop a vote. Better Together, anyone?

Conservatives

�¢ Riven by internal discord in his party, Tory leader David Cameron has promised an in/out referendum by 2017. First, however, he wants to use the threat of that vote to negotiate a better deal for the UK.

�¢ The party wants to resist further integration in the bloc and any moves to bring Britain closer to - or in to - the Eurozone.

�¢ Tories want to replace the Human Rights Acts, which enshrines the European Convention of Human Rights in England and Wales, with a British Bill of Rights.

SNP

�¢ Scottish Nationalists remain firmly in favour of "independence in Europe" - to use an old slogan - and don't want a referendum on EU membership;

�¢ If there is a vote, SNP leader Nicola Sturgeon has suggested that each of the four nations of the UK should have a veto on membership. This stance is backed by Welsh allies Plaid Cymru;

�¢ The SNP, however, wants its ministers, rather than UK ones, to have a bigger say in EU matters that affect Scotland most, such as the common fisheries policy.

Labour

�¢ Labour supports the EU and says there should only be an in/out vote if there are substantial changes to the terms of Britain's membership. It calls this its "lock";

�¢ The party, however, does want to reform the Common Agricultural Policy, impose tougher budget discipline on the EU and - in related matters- change the rights to benefits of recent migrants from EU countries.

�¢ Labour believes that Britain has become marginalised in the EU by its Eurosceptic stance and that - under Ed Miliband - the UK could take on a greater leadership role in the bloc.

Liberal Democrats

�¢ Traditionally pro-EU, the Liberal Democrats have said they believe a Brexit vote is a "threat to economic stability" and only want a referendum if there are meaningful new powers transferred to Brussels;

�¢ However, the party, when challenged, has refused to describe a Tory plebiscite as a "deal-breaker";

�¢ Liberal Democrats favour some reforms of the EU - to cut inefficiency and give national parliaments more scrutiny powers - while also strengthening EU co-operation on crime, climate and meeting foreign policy challenges in Russia, North Africa and Middle East.

UKIP

�¢ The UK "Independence" Party doesn't think Britain's place in the EU can be renegotiated; like the Tories, it backs a referendum but will urge an "out" vote regardless of any reform deal that is brokered.

�¢ The party wants to see all legislation repatriated to Westminster with a special emphasis on what it regards as EU "red tape" on businesses.

�¢ UKIP believes it can negotiate a free trade agreement with the EU after Britain exits but wish to refocus trade on traditional partner sin the Commonwealth and the US.

DUP

�¢ Northern Ireland's biggest party says it wants a referendum on the EU as quickly as possible, regardless of who is in power. It has previously suggested a vo9te as soon as 2016, ahead of the Tory target of 2017. This policy appears to be a red line in any deal in the Commons.

�¢ DUP want to renegotiate Britain's position in the EU rather than leave - but are more Eurosceptic than the Conservatives and sound more likely to live up to threats to leave.

�¢ The party has a strong track record of campaigning against EU military integration and "ever closer union".