WHEN Scots go to the polls in May to elect a new Holyrood Parliament for the next five years, they will be invited to vote not once, but twice.

Their “first” vote will be a relatively familiar affair. It will be an opportunity to cast a vote for whichever candidate the voter would like to represent their own constituency – of which there are 73 across the length and breadth of Scotland. In each constituency the winner will simply be the candidate with the most votes.

The “second” vote, on a separate ballot paper, is rather different. The paper contains lists of candidates, one list for each party contesting the election. Voters are invited to vote for one of those lists. In so doing they can either vote for the same party as that of the candidate they have backed on the constituency vote, or for a different party.

Who gets to be a MSP as a result of these list votes – and a grand total of 56 are elected via this route – is also more complicated. Moreover, it is a process that means a party that is very successful in getting constituency MSPs elected may gain little if any reward for the list votes it obtains.

The 56 additional seats do not just go to whichever party comes first. They are not even simply divided between the parties in proportion to the share of the list vote they obtain. Rather they are allocated to the parties – separately in eight different regions – so that the total number of seats – constituency and list – won by each party is in proportion to their share of their list vote in that region.

That means if a party wins a lot of constituency seats in a region, it may have already won (at least) its proportionate share of seats – and thus not be entitled to any of the list seats.

Consider, for example, what happened in the Lothian region (that is Edinburgh and its immediate environs) at the last election in 2011. The region contains nine constituencies, while there are seven additional list seats to be allocated, making a grand total of 16 seats

The SNP won eight of the nine constituency seats in the region, while winning 39.2 per cent of the list vote across the region as a whole.

So in the Lothians the party won half of all the seats in the constituency contests alone, far more than its share of the list vote. Consequently it was not allocated any MSPs when the additional seats for the region were doled out. Not a single one of the list votes cast for the SNP made a difference to the outcome.

If the polls are to be believed, this could be the prospect facing the SNP across most of Scotland in May.

Consider, for example, the most recent poll conducted by Panelbase. It suggested that if the Holyrood election were held now, then on the constituency vote the SNP would top the poll with 50 per cent, while the Labour party would be left trailing on 21 per cent, the Conservatives on 17 per cent and the Liberal Democrats on just six per cent. Compared with what happened in 2011, these figures suggest the SNP vote would be up by five points and the Conservative tally by three points. At the same time the Liberal Democrats’ score would be down by one point, while Labour’s vote would slump by no fewer than 11 points.

If those movements since 2011 were to be reflected in each and every constituency in Scotland, the SNP would scoop up no fewer than 66 constituency seats, the Conservatives would secure five, while the Liberal Democrats would retain their two outposts in the Northern Isles. Labour would emerge empty-handed, while the SNP would have secured an overall majority before a single list vote had been allocated.

But, again making the same assumption that the changes in party support since 2011 occur uniformly across Scotland, the SNP would not pick up many list seats, even though the same poll suggested they would win 48 per cent of the list vote, only slightly less than their projected share of the constituency vote and four points up on their list share in 2011.

This is because in no fewer than five of the eight regions the party would have won its proportionate share of seats (or more) via the constituency contests alone. None of the list votes in those five regions would help to elect an SNP MSP.

Only in the South of Scotland, the Highlands and Islands, and the North East would the party be allocated any list seats. Between them these three regions would send another seven MSPs to Holyrood, making a total of 73.

The possibility that many a SNP list vote will do the party little good has led to speculation that, perhaps in some regions at least, SNP supporters would be better off backing on the list vote an alternative that is also supportive of independence, such as the Greens, Tommy Sheridan’s Solidarity Party or the new left-wing movement Rise. There has even been a suggestion that the SNP should put up regional lists under a different name so that the seats the SNP won in the constituencies would not count against these lists’ entitlement when it came to the allocation of the additional seats.

THAT last suggestion is not a new one. Difficult though it might now be to believe, in the early days of devolution Labour used to find itself in much the same position in a number of regions, such as Glasgow and the West of Scotland. It was suggested then that rather than standing regional lists in its own name, Labour should get its supporters to instead back lists that stood in the name of its close ally, the Co-operative Party.

In the event nothing came of the suggestion. No doubt if such a ruse were ever attempted the Electoral Commission, the body responsible for the registration of political parties and monitoring how they spend their money at election time, might have something to say about two parties that were posing as independent organisations while colluding with each other and campaigning together.

But that still leaves open the option that SNP supporters might want to consider casting their list vote for one of Scotland’s other pro-independence parties. However, it is only worth doing so if those parties themselves have at least a chance of winning a list seat.

Given that each region has a grand total of between 15 and 17 (constituency and list) seats, a party usually has to win between five and six per cent of the list vote to win at least one additional seat.

At the moment, neither Rise nor Solidarity appears to be in that position. Panelbase’s recent poll (which named Rise as one of the options) found just one per cent support for the new left-wing movement. Solidarity has long barely registered in the pollsters’ tally at all.

In the case of the Greens, however, the position is rather different. The party already has two MSPs, one in Glasgow and one in Lothian. But with only a little more than four per cent of the list vote across Scotland as a whole in 2011, elsewhere it missed out.

Recent polls suggest the Greens might do at least a little better this time, scoring somewhere between five and nine per cent on the list vote. Many of these polls suggest it is already the case that this support consists disproportionately of voters who say they will vote for the SNP on the constituency vote.

If the Greens were to win, say, seven per cent, they could expect to pick up a seat in most of Scotland’s eight regions, as indeed the party managed to do in 2003. In some cases their chances of doing so might well be materially improved if some SNP voters backed them on the list vote.

But now comes the note of caution. The polls find it relatively difficult to measure party strengths on the list vote. When they ask people how they would vote on a second ballot paper there is a risk that some respondents, forgetful of how the system works, name the party that is their second preference when in practice they will not vote differently on the two ballots.

As a result, the polls are at risk of overestimating Green support – as they all did to some degree at the last Holyrood election. The party may not be so well-placed as it seems to pick up list votes.

Meanwhile, of course, there is no guarantee that the SNP’s current standing in the polls of 50 per cent or more will necessarily sustain itself through to polling day. If its lead over Labour were to narrow then its tally of constituency seats would fall, leaving it reliant on list seats to secure an overall majority.

Even with the 45 per cent of the vote it won in 2011, the Lothian region was the only one where the SNP did not pick up at least one seat.

So maybe it will prove to be the case that many a list vote for the SNP fails to bring the party any advantage, whereas if those votes had been cast for the Greens they might have given them a worthwhile boost. But there is no guarantee this will prove to be the case. Those SNP supporters who are thinking of “lending” their second vote elsewhere will eventually have to decide whether they think the ploy will be worth the risk.

Lending list vote to SNP’s rivals is not without risk, warns pollster

The National View: Pollster’s findings show we must vote with care