The unprecedented fragmentation of politics is one big reason the 2019 election is so hard to predict. The national result will hinge on very different sets of contests being fought across our fractured nation. Here are some of the key battlegrounds.

1. Labour Leave seats



As in 2017, a central plank of the Conservative strategy is winning over a swath of traditional Labour seats that voted heavily for Brexit. The Conservative campaign has conjured into existence “Workington Man” – an older, socially conservative, Leave-voting, long-tem Labour supporter from the Cumbrian former mining town who is taken as personifying the kind of voter they need.

The problem for the Conservatives is there isn’t much low-hanging fruit here. Taking a seat like Workington, with a majority under 10%, would probably be the bare minimum Boris Johnson needs to do to cling on. If he wants to return with any kind of majority, he will need to make inroads in Labour strongholds such as Sedgefield or Bolsover, where close to 70% of voters backed Leave but which have not returned Conservative MPs since the 1930s.

Much will turn on whether enthusiasm for Brexit and antipathy towards Jeremy Corbyn will prove sufficient to overcome generations of anti-Tory sentiment in such seats. Nigel Farage’s announcement last week that the Brexit party will contest all such seats will make this tougher, as this is likely to hit the (strongly Leave) local Conservative vote harder than the (usually Remain-leaning) local Labour vote.

Facebook Twitter Pinterest Shirebrook, in the constituency of Bolsover, a Tory target because of the huge vote in favour of Brexit in the 2016 EU referendum. Photograph: Christopher Thomond/The Guardian

2. The ‘reverse race’ in traditional marginals



Less discussed, but equally crucial, are the traditional marginal seats with small majorities and mixed populations. There are dozens of Labour- and Conservative-held marginal seats with no clear Brexit “lean”, such as High Peak, Worcester and Weaver Vale. With both parties set to lose ground on their 2017 high points, such seats will often be “reverse races”, where victory goes to the party that manages to lose the least ground to the rising Leave or Remain insurgent.

At present, that looks likely to be the Conservatives, who have recovered much of their loss to the Brexit party since the summer, while Labour face major defections to the Liberal Democrats. But that may change. As Remain voters become aware of the local tactical context, they may decide that a vote for the Lib Dems is effectively helping Johnson into No 10. Conversely, weeks of “Brexit betrayal” rhetoric may convince harder-line, “no deal” Leave voters that a vote for the Brexit party is worth the local risk in order to send a clear message to the political class.

Facebook Twitter Pinterest Worcester is a traditional marginal constituency, where both main parties face losing votes to Leave or Remain insurgents. Photograph: Alamy

3. The Tory Remain flank



While the Conservatives will be looking to advance in Leave territory, Labour and the Liberal Democrats will seek gains on the Tory Remain flank. The most vulnerable part of this flank is seats the party is defending from the Liberal Democrats – a Lib Dem vote is more attractive than a Labour one to Tory Remainers on both Brexit and domestic-politics grounds. There are a couple of dozen Conservative seats with a Remain skew where the Lib Dems either start in second or where history and local-elections strength suggest they could be in contention – typically, wealthy suburban places such as Winchester or St Albans.

There are also many seats in Remainia where the Conservatives will be fending off a Labour challenge. While direct Conservative-to-Labour switching may seem less likely, plenty of it happened in the last election, and many of these formerly safe seats are now much more vulnerable. Labour can gain more from a small swing in Remain seats than the Conservatives can gain from a small swing in Leave seats.

Facebook Twitter Pinterest Even solid Labour seats such as Manchester Withington could see a surge to the Lib Dems by disgruntled Remainers. Photograph: John Fryer/Alamy

4. Red Remain redemption?



Much of the Remain vote is densely packed into Labour-held city-centre and university seats that support EU membership by landslide margins. The Liberal Democrats will hope to exploit their surging support with Remainers in these Remain bastions, exploiting disappointment with Labour to open up a second front. Tactical-squeeze arguments will not work in such seats, as typically the Conservatives are completely out of the running, so intense Remainer disappointment with Brexit obfuscation could pose serious risks for Labour even in apparently rock-solid seats such as Manchester Withington or Hornsey and Wood Green.

5. Scotland



While some voters live in marginal seats, Scots live in a marginal country. Most Scottish seats would change hands on a small swing, virtually none are safe, and many are three- or even four-horse races. The Conservatives face a tough battle to hold on to their 2017 gains against a resurgent Scottish Nationalist party, while the Liberal Democrats will hope for gains too, given Scotland’s strong Remain lean.

6. Wales and Northern Ireland



The other smaller nations of the UK will also be hotly contested. Labour support has slumped in Wales, opening up opportunities for the Conservatives, the Liberal Democrats and Plaid Cymru. Tactical alliances between Remain or Leave parties could prove crucial here in chaotic four- or five-party contests. Northern Irish polling suggests the DUP and Sinn Féin could find it hard to replicate their 2017 clean sweep. This could have crucial implications for the Westminster balance of power if DUP MPs are replaced by others less sympathetic to the Conservatives or Brexit, or if Sinn Féin MPs who never take their seats in parliament are replaced by pro-Remain MPs who do.

7. Independents and wildcards



Thanks to unprecedented churn in this turbulent parliament, there will be an unusually large crop of high-profile MPs standing as independents, or standing for new parties (and often in new seats). Their presence on the ballot adds a wildcard element to many contests.

For example, Luciana Berger’s presence on the ballot as a Liberal Democrat gives the party a chance in Finchley, a seat that would otherwise be hopeless for it. Sam Gyimah and Chuka Umunna could lift Lib Dem prospects elsewhere in London. Labour’s prospects for Broxtowe will be boosted by former Tory Anna Soubry’s presence on the ballot as a Change UK candidate. Dominic Grieve’s Lib Dem-supported run as an independent puts the otherwise rock-solid Conservative seat of Beaconsfield into play, and former MPs running under various banners will complicate Labour’s defences of various seats.

Rob Ford is professor of political science at the University of Manchester