MEPs are elected using the d'Hondt method, meaning each party's total number of votes is divided by 1, then 2, then 3, all the way up to n, where n is the number of total seats being allocated. So if a party gets 1000 votes, in round 1 it has 1000, in round 2 it has 500, in round 3 it has 333, round 4 it has 250, and so on. Note that in each round, you're dividing the full total, not the result of the previous round. So, here were 2009's results, with the 6 rounds of division:
The numbers in bold represent the seats allocated in 2009. The numbers in italics represent the seats that would have to be allocated in order for UKIP to get an MEP. Here are those numbers in graphical form (minus the ones below UKIP):
They barely even got a quarter of Labour's votes, and Labour got almost 100,000 votes less than the SNP in 2009. And just to spell it out, here's the order MEPs would be elected in order for UKIP to get in:
5. Lib Dem
13. Lib Dem
In fact, even if every BNP voter had voted for UKIP instead (after all, they're basically the same thing), there would still need to have been 9 MEPs for UKIP to get a look in.
Now, obviously the 2014 results will not be the same as the 2009 results. The Lib Dems are likely to lose a substantial number of votes, perhaps as many as 60,000 if their performance in 2011 is to be repeated. They could drop below the Greens, and who knows, maybe even UKIP. But that doesn't automatically mean there's a seat going begging for whoever can finish fourth in terms of the total vote. Even at the third round of dividing, the SNP's vote was still almost 50,000 higher than UKIP's total vote in 2009. UKIP would need pretty much all those former Lib Dem voters to come over to them, which seems rather unlikely - after all, if you were annoyed at the Lib Dems for putting a right-wing party into government at Westminster, why would you then vote for a party which is even more right-wing? Especially as the two parties are diametrically opposed when it comes to the EU.
The reality is that, although UKIP's vote has been growing across the UK as a whole, in Scotland they have already started losing votes. They lost 1.5% in 2009, which is interesting when you consider that the Lib Dems lost 1.6%, which suggests that ex-Lib Dem voters don't go flocking to UKIP in Scotland. Contrast that with the Scottish Greens, who have been on the rise constantly. It seems likely from this picture that any ex-Lib Dem voters are more likely to go to other pro-EU parties (unless some of them went to the BNP, although that'd be a bit weird...) In fact, it seems more likely that UKIP's surge in 2004 was at least partly down to Eurosceptic SNP voters unhappy with the strong pro-EU stance John Swinney took in 2004 (if my memory serves me correctly, that is - I seem to recall a series of televised debates, devoting one to each leader, with Swinney being very committed to Scotland joining the Euro, which probably pissed off the SNP fundies...) Such people are unlikely to ditch the SNP with the referendum so close.
The picture is different across the UK as a whole. UKIP clearly benefit from ex-Tory voters, with the Tories managing to shore up their vote in 2009 thanks to people indicating to Labour that they were on their way out of Westminster in 2010. UKIP will doubtless receive another surge in support in 2014, both from anti-EU Tory voters with the EU referendum in mind and from the kind of folk who voted BNP in 2009 because of their anti-immigration rhetoric, rather than "the old racism" stuff (the BNP appear to be pretty much dead, as their MEP-who-isn't-Nick-Griffin now leads his own brand new racist party, and they absolutely bombed in the 2012 local elections in England). Left-wing Lib Dem voters will probably go to Labour, even though they should really go to the Greens.
Quite simply, the 2014 European Election will almost certainly serve only to highlight yet again the differing politics in Scotland and the rest of the UK. It will be a tale of two referendums: in England (and perhaps Wales - UKIP have a Welsh MEP, after all), the focus will be on the EU referendum; in Scotland, we'll all be focussing on the Independence referendum. These are the prisms through which people will be looking when deciding who to vote for in May, and they will yield very different results north and south of the border. It all hinges on the Tory vote, really - in England, you get the feeling there's a sizeable chunk of Tory voters who will ditch the party for UKIP in order to force the issue of the EU referendum; but in Scotland, you get the feeling the Tories are pretty much at their base support already, and they're certainly not going to ditch them for a party that has no chance of getting an MEP.
And all this is before you even consider the fact that UKIP's candidate selection process in Scotland has been a disaster, or that the SNP are currently polling well above the 29.1% they got in 2009 in both Westminster and Holyrood voting intentions...