Also, however, it is one of eight constituencies in the Mid and West Wales electoral region, which elects four additional members, in addition to eight constituency members, to produce a degree of proportional representation for the region as a whole.

The region consists of the eight constituencies of Brecon and Radnorshire, Carmarthen East and Dinefwr, Carmarthen West and South Pembrokeshire, Ceredigion, Llanelli, Meirionnydd Nant Conwy, Montgomeryshire and Preseli Pembrokeshire.

The other four Dyfed constituencies were, again, Carmarthen East and Dinefwr, Carmarthen West and South Pembrokeshire, Ceredigion and Preseli Pembrokeshire, all within the Mid and West Wales electoral region.

The region consisted of the constituencies of Brecon and Radnorshire, Carmarthen East and Dinefwr, Carmarthen West and South Pembrokeshire, Ceredigion, Dwyfor Meirionnydd, Llanelli, Montgomeryshire and Preseli Pembrokeshire.

For Westminster purposes, the same new constituency boundaries became effective for the 2010 United Kingdom general election.