Show caption There is a two million majority against Boris Johnson’s Brexit plans – but voters need to think tactically in target seats. Illustration: The Observer Tactical voting Tactical voting guide 2019: the 50 seats where it is vital to keep the Tories out One of Britain’s leading pollsters identifies the best choices for Remain voters at key general election battlegrounds Peter Kellner Sun 8 Dec 2019 07.57 GMT Share on Facebook

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On current trends, voters will deliver a contradictory verdict on Thursday night. The Conservatives are on course for an overall majority in parliament – but most voters will back parties that want to block an early Brexit. If turnout is similar to last time, the 14 to 15 million who will support the Conservatives or Brexit party will be outnumbered by the 16 to 17 million who will vote Labour, Liberal Democrat, Green, SNP or Plaid Cymru.

Tactical voting is not new, but it has a special significance this week. If it happens in enough constituencies, it can ensure that the two-million majority opposed to Boris Johnson’s Brexit plan is reflected in the new House of Commons.

The map below shows 50 seats where tactical voting could keep the Conservatives out. Most tactical voting websites draw on one or two sets of polling data, which risk ignoring the specific circumstances of individual constituencies. The guide draws on a wider range of information – detailed big-sample national polls, but also constituency surveys (including those reported week by week in the Observer), past election results and local activity, such as the recent student registration drives in some key seats (one is Brunel University, in Johnson’s own constituency, Uxbridge).

The three latest constituency surveys underline the potential impact of tactical voting. Putney, Southport and Guildford all elected Conservative MPs last time, despite voting heavily to remain in the 2016 referendum. Currently, the Conservatives lead Labour in Putney (by 3%) and Southport (by 8%). Guildford is almost neck-and-neck between the Lib Dems (41%) and the Conservatives (40%). Given margins of error on local surveys with samples of 500, all three seats are in play. Enough tactical votes for Labour in Putney and Southport, and the Lib Dems in Guildford, could defeat the Tories in all three seats.

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However, without tactical voting, these three seats – like many others – may well return pro-Brexit MPs, despite having clear Remain majorities, because of the way the anti-Conservative vote divides.

In the map, each choice is briefly explained. The 50 seats include 33 in England and Wales that elected Tory MPs last time. The Lib Dems are recommended in 18 seats, Labour in 13 and former Conservatives in two: Dominic Grieve and David Gauke, now standing as independents and backed this weekend by John Major. (Another former Tory backed by Major, Anne Milton in Guildford, has only 7% support in our latest poll. Major’s support risks siphoning votes from the Lib Dems, and letting the Conservatives retain the seat.)

It should be stressed that there are many other marginals where Labour is the clear challenger to the Conservatives, but in almost all of these seats the Lib Dems are out of the running. There is little need here for a tactical guide to recommend Labour.

In general, where the incumbent MP is Labour, they are the best placed to keep out the Tories. There are four exceptions: two in Scotland and one each in England and Wales. Here, without tactical support for the best-placed non-Labour candidate, Conservative gains are a real possibility. However, in two three-way marginals, Labour needs to win over local supporters of the Lib Dems (Portsmouth South) and Plaid Cymru (Ynys Môn) to be sure of defeating the Conservatives.

Scotland presents a specific challenge. A number of traditional Labour strongholds went SNP in 2015 and then Conservative in 2017. In these – as well as Gordon, a former Lib Dem seat, and Moray, once an SNP bastion – the SNP are now best placed to see off the Conservatives.

Peter Kellner is a polling expert and former president of YouGov

Top targets

SCOTTISH CONSERVATIVE SEATS VULNERABLE TO THE SNP

1 Aberdeen South

A Labour seat until 2015, the SNP now has the best chance of overturning a Conservative majority of almost 5,000 VOTE SNP

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2 Angus

The SNP needs to squeeze the Labour vote to regain one of its former strongholds VOTE SNP

3 Ayr, Carrick and Cumnock

Three-way contest in 2017, with Labour now in third place VOTE SNP

4 Banff and Buchan

The SNP’s Paul Robertson needs to squeeze both Labour and Lib Dem support to overturn a Tory majority of almost 4,000 VOTE SNP

5 Dumfries and Galloway

One-time Labour seat won by the SNP in 2015 and the Tories in 2017. Labour is now trailing; the SNP has the best chance VOTE SNP

6 East Renfrewshire

Three-way marginal, Labour until 2015, but the SNP is now established as the local challenger to the Conservatives VOTE SNP

7 Gordon

Lib Dem-held for 32 years until 2015, but they came fourth in 2017 VOTE SNP

8 Moray

In 2017, the Tories unseated Angus Robertson, SNP leader in the Commons; the SNP needs to overturn a 4,000 majority VOTE SNP

9 Ochil and South Perthshire

The SNP is seeking to squeeze the Labour vote, which totalled almost 11,000 last time, to regain a seat they won in 2015 VOTE SNP

10 Stirling

Historically a Tory-Labour marginal, the SNP now has the best chance of overturning a Conservative majority of just 148 VOTE SNP

LABOUR MARGINALS IN SCOTLAND

11 East Lothian

A three-way marginal last time, the SNP has the best chance of stopping the Conservatives gaining a seat they have never won before VOTE SNP

12 Kirkcaldy and Cowdenbeath

Gordon Brown’s seat until the SNP gained it in 2015 before losing it to Labour, very narrowly, in 2017. This time, the SNP candidate has been sacked for posting antisemitic material online VOTE LABOUR

13 Midlothian

One-time safe Labour seat, now a three-way marginal where a split anti-Brexit vote could let in the Tories VOTE SNP

ENGLISH CONSERVATIVE SEATS VULNERABLE TO TACTICAL VOTING

14* Beaconsfield

Running as an independent, Dominic Grieve is defending the seat he won as a Conservative VOTE INDEPENDENT

15 Cheadle

The Lib Dems hope to regain a seat they held from 2001 to 2015 VOTE LIB DEM

16* Chelsea and Fulham

City “superwoman” Nicola Horlick is standing for the Lib Dems against anti-Brexit Tory Greg Hands in a strongly Remain seat VOTE LIB DEM

17 Cheltenham

Lib Dems hope to regain a Remain seat they lost in 2015 to Alex Chalk, who backed Remain in the Brexit referendum VOTE LIB DEM

18 Chingford and Woodford Green

Big swings to Labour in 2015 and 2017 have turned Iain Duncan Smith’s once-safe seat into a marginal VOTE LABOUR

19 Chipping Barnet

Pro-Brexit Theresa Villiers is defending a 353 majority in a seat that voted Remain VOTE LABOUR

20* Cities of London and Westminster

The former Labour MP Chuka Umunna is standing as a Lib Dem VOTE LIB DEM

21* Esher and Walton

Dominic Raab is at risk in this Remain seat despite a 23,000 majority VOTE LIB DEM

22 Filton and Bradley Stoke

A large student population in this seat could help Labour overturn a 4,000 Conservative majority VOTE LABOUR

23* Finchley and Golders Green

Former Labour MP Luciana Berger is standing as a Lib Dem candidate in a seat where Labour’s antisemitism problem has hit hard VOTE LIB DEM

24* Guildford

A Lib Dem target also being contested by ex-Tory Anne Milton, who is now standing as an independent VOTE LIB DEM

25 Hazel Grove

Former Lib Dem seat; a 5,500 Tory majority would be overturned if Labour supporters (9,000 last time) voted tactically VOTE LIB DEM

26* Hendon

The Lib Dem challenge has faded in this Tory-Labour marginal VOTE LABOUR

27* South West Hertfordshire

Independent David Gauke is defending the seat he won as a Conservative VOTE INDEPENDENT

28 Lewes

Lib Dems hope to regain a seat they held between 1997 and 2015 from Maria Caulfield, who resigned as Conservative vice-chair in protest against May’s Brexit deal VOTE LIB DEM

29 Loughborough

The local student vote could threaten a 4,000 majority; the former MP, Nicky Morgan, is not standing VOTE LABOUR

30* Putney

The Lib Dem challenge has not materialised in this Con-Lab marginal VOTE LABOUR

Phillip Lee, now a Liberal Democrat, is challenging arch-Brexiter John Redwood in Wokingham. Photograph: Ray Tang/Rex Shutterstock

31 Richmond Park

Zac Goldsmith’s 45-vote majority is vulnerable to the former local Lib Dem MP Sarah Olney VOTE LIB DEM

32 Rushcliffe

Ken Clarke’s 8,000 majority is vulnerable; he is standing down and the Conservative candidate, Ruth Edwards, is pro-Brexit in a Remain seat VOTE LABOUR

33 South Cambridgeshire

Local former Conservative MP Heidi Allen is standing down; she supports the local Lib Dem candidate VOTE LIB DEM

34* Southport

A three-way marginal that the Lib Dems lost to the Tories in 2017 VOTE LABOUR

35 St Albans

A strong Remain seat where the Lib Dems have built a strong local base VOTE LIB DEM

36 St Ives

Andrew George hopes to regain a seat he held for the Lib Dems from 1997 to 2015 VOTE LIB DEM

37 Totnes

Sarah Wollaston is standing as a Lib Dem in the seat she held for nine years as a Tory VOTE LIB DEM

38 Truro and Falmouth

Labour has the best chance in an area that used to vote Lib Dem VOTE LABOUR

39 Uxbridge and South Ruislip

Boris Johnson’s 5,000 majority could just be vulnerable to a large Labour vote by Brunel University students VOTE LABOUR

40 Wantage

Ed Vaizey, ex-minister and critic of Johnson, is standing down in a seat with a growing Lib Dem challenge VOTE LIB DEM

41 Watford

Labour has the best chance of retaking the seat, despite a Lib Dem challenge, to overturn a 2,000 Tory majority VOTE LABOUR

42* Wimbledon

The Lib Dems are now the challenger in a strongly Remain seat VOTE LIB DEM

43 Winchester

Lib Dems hope to regain a seat they held from 1997 to 2010 VOTE LIB DEM

44 Wokingham

Arch-Brexiter John Redwood faces Phillip Lee, who switched from the Tories to the Lib Dems, in this Remain seat VOTE LIB DEM

45 Wycombe

There’s an outside chance of an upset in this once-safe Tory seat held by the ERG leader, Steve Baker VOTE LABOUR

46 York Outer

Students voting tactically could put an 8,000 Tory majority at risk VOTE LABOUR

ENGLISH AND WELSH LABOUR SEATS NOW THREE-WAY MARGINALS

47* Kensington

Former Tory MP Sam Gyimah is standing as a Lib Dem; Labour is now third, polls say VOTE LIB DEM

48* Portsmouth South

Three-way marginal held by the Tories, Labour and Lib Dems in recent years VOTE LABOUR

49 Sheffield, Hallam

Labour’s controversial Jared O’Mara is standing down after winning the seat from Nick Clegg in 2017 VOTE LIB DEM

50 Ynys Môn

A three-way marginal between Labour, the Tories and Plaid Cymru VOTE LABOUR

* Seats with Deltapoll surveys reported earlier in the Observer