The Conservatives have made steady advances in the East Midlands at recent general elections and now hold almost every constituency in the region – but in doing so they have given themselves a large number of marginal seats to defend.

A redrawing of boundaries means the East Midlands now has 47 constituencies, up from 46 in 2019, and, had the last election been fought on these new boundaries, it is calculated the Tories would have won 39 seats and Labour eight.

Notional results for the 2019 election based on the 2024 boundaries have also been calculated, in order to determine the scale of the challenge facing candidates this time, and it is these notional majorities that are used below.

There are 11 seats in the East Midlands where the Tories are defending majorities of just under 10,000, starting with High Peak, where the majority is just 590.

Some of these seats were held by Labour until as recently as 2019, such as Gedling (Tory majority 2,407) and Ashfield (5,303).

Others are so-called “bellwether” seats, which means the result in the constituency has a habit of matching the overall result of the general election – such as Northampton North and Loughborough, both of which have been bellwethers since the election of February 1974.

Such a high number of marginal seats means the East Midlands is likely to play a pivotal role in determining the make-up of the new House of Commons.

The contest in Ashfield will be particularly closely-watched, where its former MP Lee Anderson – who defected from the Conservative to Reform during the last parliament – is standing for Reform against a new Tory candidate, along with a candidate from the Ashfield Independents who run the local council (and who came second in the seat in 2019), plus Labour, the Liberal Democrats and the Greens.

If Labour manages to push the swing from the Conservatives across the region up to 15 percentage points, a total of 16 seats could change hands, with Harborough, Oadby & Wigston the 16th to fall.

This is a constituency that ranks at number 174 on Labour’s UK-wide target list, and is a seat that has been held by the Tories continuously since 1950.

The eight constituencies Labour are defending in the East Midlands are all clustered around the cities of Leicester (Leicester East, Leicester South, and Leicester West), Nottingham (Nottingham East, Nottingham North & Kimberley, and Nottingham South) and Derby (Derby South), along with the town of Chesterfield.

A measure of Labour’s success or failure in the region will depend on how well it is able to break out of these urban strongholds and into less densely-populated surrounding areas.

Voters in Leicester East are in the unusual position of being able to choose between the official Labour candidate, Rajesh Agrawal; two former Labour MPs who once represented the seat, Claudia Webbe (Independent) and Keith Vaz (One Leicester Party); plus seven other candidates.

The Lib Dems came second in two seats in the East Midlands, according to the 2019 notional results: Hinckley & Bosworth and Rutland & Stamford.

Both of these constituencies would need enormous swings from the Tories to the Lib Dems to change hands – 23.3 and 23.8 percentage points respectively – and as such it would take an exceptional performance by Sir Ed Davey’s party to win either of them.

– All notional majorities and swings mentioned above have been compiled by Professors Colin Rallings and Michael Thrasher of the University of Plymouth, on behalf of BBC News, ITV News, Sky News and the PA news agency, and will be used as the basis for reporting the gains and losses at the General Election.