By Lewis Baston

The European elections are tricky for Remainers. Change UK, the Greens and the Lib Dems are vying for their votes. There are plenty of good Remain campaigners in Labour, even if the leadership equivocates on a second referendum. And many are concerned about voting in the wrong way and letting Nigel Farage get extra seats.

Figuring out how to vote became a lot easier after the publication of new large-scale polling data from Best for Britain over the weekend providing detailed information for each of the 11 electoral regions in Great Britain.

It's still not watertight, however. Polling is an uncertain science, and in times like this - when opinion is volatile, there are new parties and nobody can be sure about turnout - it is particularly tricky to get an accurate read on what is going on. Everything in this article comes with a health warning about the certainty of the information on offer. But using this data we can get a clearer picture of what's going on in each region and how Remainers can maximise their vote.

How the European elections work

The European elections use a kind of proportional representation system called D’Hondt. There are nine English voting regions and one each for the other nations. Each region has a number of MEPs that reflects the number of people living there – from three in the North East to ten in the South East.

After the votes are counted, the seats are allocated to parties in order using a formula. The lead party is given a seat, then their support is cut by half. So if Labour was the lead party with 30%, it would be given a seat, then have its support slashed to 15%. Then officials would look at who was next and give them a seat. If no party got more than 15%, Labour would get a second seat and its support would be slashed again. And so on until you fill all the seats.

Party candidates are elected in the order they appear on the list – if the party gets one seat, the candidate who is first on the list is elected, and so on. Each party therefore has a 'leading candidate', 'second candidate', 'third candidate' and so on.

One word of warning on the guide below. Proportional representation makes tactical voting much harder. In actual fact that is one of the arguments for using it. The margins between the parties for the last seat or two in each region are narrow and that makes things difficult. Using some pretty rough polling to make fine decisions is not going to be entirely reliable and scientific. The advice given here assumes that YouGov are on the right lines. They may not be.

If in doubt, go with your heart and vote for whichever party most represents your beliefs.

And finally, there is nothing you can do in this election which is more important than increasing turnout. Go and vote, and encourage others to do so.

REGION BY REGION

How to read the regional tables

Not all tactical voting is the same. You need to ask yourself what you are trying to achieve.

Maybe you want a big vote for a single strong Remain party, to catch the media's attention. If so, vote Liberal Democrat. There's no need to go into any regional details.

Many people will be simply trying to get MEPs from Remain-supporting parties elected. Those parties are the Liberal Democrat, Green, Change UK, SNP and Plaid Cymru. If so, follow the recommendation for 'Maximise full Remain seats'.

If your priority is to minimise the number of Brexit party seats, then there will be regions in which voting Labour - or even Conservative - is the most likely way of knocking out the most marginal Brexit party candidates. This advice is given under 'Minimise Brexit Party seats'.

There's also a final 'Lifesaver' column. This is basically a guard against being too clever. If you are OK with the party it mentions, you should definitely vote for them, because they are at risk of losing a seat. In some areas, it refers to the Greens. But in many it refers to Labour. Lots of Remainers struggle with this because of the party's will-they-won't-they attitude to Brexit, but there are many dedicated Remainers running on the Labour tickets, up against implacable Brexit party candidates. For those who are broadly tolerant of the party, it indicates where they're in trouble and needing support.

Northern Ireland is not included because it uses a different electoral system, called STV-PR. Voters in NI don't have to vote tactically and several pro European options are available.

NORTH EAST

Because the North East only has three MEPs, few parties have a chance of winning a seat and the tactical position is simpler. One seat goes to the Brexit party, one to Labour and the third on current form to the Brexit party. While the second Brexit party seat is the most marginal, it is not very marginal – Labour are nine points behind and the Lib Dems are 5.5 points behind. It is a long shot, but if Green and Change UK supporters want to deprive Farage of a seat here they should lend their votes to the Liberal Democrats.

Labour Remainers might want to stay with Labour in the hope that the poll is too pessimistic and that they might hope to re-elect Paul Brannen, a good MEP who has endorsed Remain Labour.

NORTH WEST

The North West is a large region (eight seats) and therefore the result is fairly proportional and the allocation of the last seats is well within the margin of polling error. The last three seats are given, on some small margins, to the Brexit party, Greens and Conservatives. Labour can be fairly sure of two seats but do not look like getting a third, and Change UK is well behind.

The tactical task is to get both Greens and Lib Dems ahead of the Brexit party and the Conservatives – the Conservative seat is more vulnerable than the Brexit party third seat. People currently intending to vote Green, or considering it closely, should stick with that, but the Lib Dems are more in need of tactical votes. An optimal split of tactical votes would get both parties across the line, but it is impossible to plan such things precisely in advance of the vote.

YORKSHIRE AND THE HUMBER

The Yorkshire and the Humber region only has six seats and there is a risk that the Brexit party could end up with half of those seats for only a third of the vote. Of the fully committed Remain parties, the Lib Dems are closest behind – but they need another six percentage points and it is not obvious where they can obtain them.

There is a strong case in this region for floating Remain votes to lend their support to Labour. The two leading Labour candidates are Richard Corbett and Eloise Todd, both of them committed Europeans who would add to the strength of that case in the Labour party and the UK. If you are unable to support Labour, then vote for the Lib Dems but do not be under any illusions that this tactical vote is likely to work.

EAST MIDLANDS

Of the three core Remain parties, the Greens stand the best chance of beating the Brexit party to the last seat, needing two to three percentage points more support. With Lib Dem and Labour assured of a seat each and Change UK some way short, the Greens are the obvious option in this region.

A vote for a Conservative list headed by Leave-supporting MEP Emma McClarkin cannot be recommended as a Remain tactical option, but arithmetically it is easiest for the Tories to overtake the third Brexit party candidate.

WEST MIDLANDS

In the West Midlands, think carefully about what you want to achieve by tactical voting. The last seat is very marginal between the Conservatives and the Brexit party - and it is significantly more difficult for the other parties to overhaul both parties. If making Farage less happy is your goal, then there is an argument for voting Conservative. The MEP you would help elect, Anthea McIntyre, would be a reasonable and constructive presence in the European parliament.

Voting Conservative is understandably beyond the pale for most Remainers. But if the poll is correct the other parties will need a lot of luck and tactical voting to win. The nearest to doing so is Labour – particularly if YouGov is understating the party's support. Labour's second candidate, Sion Simo, is a Remain Labour signatory.

If voting Labour is also unpalatable, the Greens might be the best bet although the difference between them and the Lib Dems is within the margin of error.

LONDON

The tactical position is not clear in London. The last two seats are due to go Conservative and Labour respectively on the basis of the large YouGov poll, although the margins over the other parties are fairly tight. The Brexit party seems assured of two seats but is a long way from getting a third.

None of the core Remain parties is all that close to winning an extra seat. The Lib Dems are about five points off overtaking Labour and about six behind pipping the Tories as well. For the Greens, the lag is six points as well. For Change UK it is four points. The most hard-core Remainers should switch to Change UK, as neither the Green seat nor the second Lib Dem seat is at risk. Getting Change UK's Gavin Esler over the threshold is the most efficient way of claiming a seat.

Labour Remainers will wish to consider that the seat at risk is that of Seb Dance, a strong pro-European voice. Protecting his position by voting Labour is therefore an attractive option. If Change UK can overtake the Conservatives and Labour gets a few more votes, the Change UK gain is made at the expense of the Tories rather than Seb Dance.

EASTERN ENGLAND

The contest for the last two seats is a close one between the Conservatives, Greens, a second Lib Dem and the fourth Brexit party candidate. Both Lib Dem and the Greens therefore need votes to ensure that they are ahead of the quota that might elect a Brexit party MEP.

If you want to play it safe, or are already intending to vote that way, you should vote Green. If you have more appetite for risk and are determined to defeat the Brexit party, then vote Lib Dem. They need another two to three percentage points to beat Farage's number four candidate here.

SOUTH EAST

Tactical voters in the South East should vote for the Liberal Democrats. They are about a point and a half away from gaining a seat at the expense of the Brexit party. Greens and Labour can both be confident of one seat but stand little chance of a second. Change UK is further behind the Brexit party, needing two to three percentage points more support to win the seat. Their strong supporters might feel they can do it but on the evidence of this poll the Lib Dems are a better hope.

SOUTH WEST

The tactical advice in the South West is clear on the basis of this poll – unless you are already intending to vote Green, then swing behind the Lib Dems. They are just a percentage point behind getting a second seat at the expense of the Brexit party. Supporters of Change UK should switch to the Lib Dems too.

For Labour it is a little more complex. Eight points seems an abnormally bad reading for Labour. Labour Remainers might view this regional sample as being a bit suspect and conclude that the party is nearer the threshold for election than it appears from this result. It would not take much poll error. The Labour slate is led by a hard-working MEP and Remain Labour signatory Clare Moody, backed up by Andrew Adonis.

SCOTLAND

The SNP is the leading Remain party in Scotland and looks as if it should get three seats without being particularly close to getting a fourth. There appears to be little chance of Lib Dem or Change UK winning a seat. The last two seats are close between Greens, Conservatives, Labour and Brexit. The Greens are ahead but well within the margin of error. Nevertheless, the best way to make sure one of the Remain parties doesn't miss out narrowly is to vote Green.

Remain voters may also want to consider giving Labour some help to stay ahead of the Conservatives and avert the risk of a second Brexit party seat. Scottish Remain supporters currently intending to vote Labour should probably stick with it. Labour’s lead candidate is David Martin, a senior figure in the Party of European Socialists and a Labour Remain signatory.

WALES

Wales is another small constituency, with four seats to be divided between the parties. On current polling there is little chance of depriving the Brexit party of its second seat. For that to happen, either Plaid Cymru or Labour have to overtake them in their total vote, or another party has to get past 17.5%. Neither of these outcomes seem likely.

Remain supporters may wish to ensure that the gap between Plaid Cymru and the Brexit party is as small as possible and therefore vote Plaid Cymru.

Labour voters who fear that the party might be falling further behind might wish to stick with it to ensure it gets a seat, especially given that the slate of Labour candidates in Wales is solidly pro-European.

Lewis Baston is a writer on politics, elections and history. You can follow him on Twitter here.

The opinions in Politics.co.uk's Comment and Analysis section are those of the author and are no reflection of the views of the website or its owners.