New Boundaries: Wales (UK) Parliamentary forecast by Electoral Calculus

Each new seat can be described as a combination of parts of old seats. These tables show this decomposition. The winner of the old seat at the 2015 election is shown by party colour, as is the implied winner of the new seat.
The implied results are calculated using the local election results for the wards which make up each old seat. This should give the most accurate projection, since it reflects varying political behaviour across the seat.

Wales Change Table

 Old SeatsNew SeatsChangeDisappearSwitch OutSwitch InFresh
The table shows how the various changes affect each party in this region. The total old and new seats are shown for each party, as well as their difference ('Change'). The change in seats is also explained through the four explanations:
  • Disappear : seats which have disappeared as they are broken into small fragments
  • Switch Out : seats lost because their political make-up has altered
  • Switch In : seats gained because their political make-up has altered
  • Fresh : freshly created new seats which are made up of small fragments of old seats
The old seats which are disappearing are: Aberavon; Aberconwy; Arfon; Cardiff Central; Carmarthen West and Pembrokeshire South; Delyn; Gower; Islwyn; Montgomeryshire; Newport East; Pontypridd.
The old seats which are lost to another party are: Bridgend; Cardiff North; Clwyd South; Vale of Clwyd; Ynys Mon.
The new seats which are gained from another party are: Bridgend and Vale of Glamorgan West; Cardiff North; Clwyd South and Montgomeryshire North; Flint and Rhuddlan; Ynys Mon and Arfon.


New seatPrimary componentSecondary component(s)
Alyn and Deeside100% of Alyn and Deeside30.8% of Delyn
Clwyd South and Montgomeryshire North56.2% of Clwyd South49.6% of Montgomeryshire
23.4% of Clwyd West
7.2% of Dwyfor Meirionnydd
3.0% of Vale of Clwyd
Colwyn and Conwy69.2% of Clwyd West80.8% of Aberconwy
Flint and Rhuddlan71.0% of Vale of Clwyd69.2% of Delyn
Wrexham Maelor100% of Wrexham43.8% of Clwyd South


New seatPrimary componentSecondary component(s)
Carmarthenshire92.4% of Carmarthen East and Dinefwr40.8% of Carmarthen West and Pembrokeshire South
Ceredigion and North Pembrokeshire100% of Ceredigion24.0% of Preseli Pembrokeshire
7.6% of Carmarthen East and Dinefwr
8.2% of Montgomeryshire
Llanelli and Lliw100% of Llanelli32.8% of Gower
Pembrokeshire South76.0% of Preseli Pembrokeshire59.2% of Carmarthen West and Pembrokeshire South


New seatPrimary componentSecondary component(s)
Blaenau Gwent100% of Blaenau Gwent48.8% of Islwyn
Caerphilly63.9% of Caerphilly46.5% of Islwyn
20.7% of Newport West
Monmouthshire87.9% of Monmouth35.9% of Newport East
Newport68.9% of Newport West64.1% of Newport East
Torfaen100% of Torfaen12.1% of Monmouth
10.3% of Newport West


New seatPrimary componentSecondary component(s)
Clwyd North and Gwynedd92.8% of Dwyfor Meirionnydd26.0% of Vale of Clwyd
25.4% of Arfon
19.2% of Aberconwy
7.5% of Clwyd West
Ynys Mon and Arfon100% of Ynys Mon74.6% of Arfon

Mid Glamorgan

New seatPrimary componentSecondary component(s)
Bridgend and Vale of Glamorgan West100% of Bridgend20.2% of Vale of Glamorgan
Cynon Valley and Pontypridd100% of Cynon Valley50.0% of Pontypridd
Merthyr Tydfil and Rhymney100% of Merthyr Tydfil and Rhymney36.1% of Caerphilly
4.7% of Islwyn
Ogmore and Port Talbot100% of Ogmore38.3% of Aberavon
Rhondda and Llantrisant100% of Rhondda45.1% of Pontypridd


New seatPrimary componentSecondary component(s)
Brecon, Radnor and Montgomery100% of Brecon and Radnorshire42.2% of Montgomeryshire

South Glamorgan

New seatPrimary componentSecondary component(s)
Cardiff North89.0% of Cardiff North37.6% of Cardiff Central
4.8% of Pontypridd
Cardiff South and East54.3% of Cardiff South and Penarth62.4% of Cardiff Central
11.0% of Cardiff North
Cardiff West100% of Cardiff West16.1% of Cardiff South and Penarth
Vale of Glamorgan East79.8% of Vale of Glamorgan29.6% of Cardiff South and Penarth

West Glamorgan

New seatPrimary componentSecondary component(s)
Gower and Swansea West83.1% of Swansea West57.9% of Gower
Neath and Aberavon100% of Neath47.0% of Aberavon
Swansea East100% of Swansea East16.9% of Swansea West
14.7% of Aberavon
9.3% of Gower