Jamie Reed. Stefan Rousseau PA Wire/PA Images LONDON — The Conservatives are favourite to win the upcoming by-election in Copeland — and the significance of this is difficult to overstate.

Bookmakers, including William Hill and Betfair, make the Tories strong favourites to nab the Cumbrian seat after it was left vacant by Labour MP Jamie Reed, who announced on Wednesday that he is resigning.

History tells us that Labour should go into Copeland expecting nothing less than victory.

Firstly, it has been a Labour seat since 1931. Copeland served as a prime example of a safe seat throughout the 20th century and well into the 21st. A Tory victory here would put an abrupt end to over 80 years of Labour dominance.

Secondly, it is pretty much unheard of for a party-in-government to gain a seat in a by-election. The last time it happened was in 1982 when a resurgent Tory government took Mitcham and Morden from Labour.

The circumstances surrounding this particular case were incredibly strange, though, as the sitting Labour MP had chosen to defect to the Social Democratic party before the by-election took place.

But in 2017 the history books could be thrown out the window, with the Tories preparing to throw everything at this by-election when campaigning gets underway — and they have every reason to do.

A constituency Labour has left behind

For decades Copeland, known as Whitehaven up until 1983, had all the ingredients for Labour victories.

A traditional industrial area, it's towns are and villages are now generally deprived and connected by transport links so neglected that it would be generous to describe them as a network. It has a proud mining heritage and strong trade union culture, the latter owing mainly to workers in the area's nuclear industry.

Pockets of loyal Tory support dotted around the Cumbrian coast meant Labour election victories were rarely massive, but as frequent as clockwork nonetheless. Copeland has been Labour since the seat's inception.

But now the political landscape is shifting under Labour's feet and Copeland is no exception.

Around 60% of people there voted for Leave in the EU referendum. Naturally, this means people there will feel more inclined to vote for the Tories, who have promised to deliver Brexit rather than Labour who campaigned against it.

Copeland is just one example of many pro-Leave constituencies in the north of England that are at risk of falling through Labour's grasp. It's a hunting ground for May and Paul Nuttall's UKIP too, although the success of the latter in targeting seats like Copeland could be undermined by the party's weak presence in the north of the country.

Labour leader Jeremy Corbyn. Reuters

Then there's the area's demographics. While Jeremy Corbyn, John McDonnell and other members of Labour's cabinet come from the London bubble, Copeland is a white, working-class area, with barely any students and lots of retired people. Polls show that Corbyn is astonishingly unpopular with elderly people, who are also more likely to vote.

To borrow a turn of phrase from Business Insider's Adam Bienkov, for many older voters in rural seats like Copeland the Corbyn-led Labour is about as appealing as "a sack of rotten fish."

Then you have the rather massive and unavoidable elephant in the room: Corbyn's anti-nuclear stance.

Copeland forms part of one of the UK's main nuclear hubs. It is where Sellafield is based, a huge nuclear plant that employs around 10,000 people, many of who live in the surrounding area. It is where Reed will take up his next job.

Copeland's loyalty to Labour is going to be severely put to the test at this by-election, which is expected to take place in February."It's up Corbyn's henchmen and women to prove now that they are capable of winning," a Labour MP told Business Insider on Thursday. If Labour loses, it'll be a historic defeat and the clearest signal yet that the party is heading for disaster at the next general election.