Notional results for a UK general election on 5 May 2005 Elections contested by Plaid Cymru
A notional general election to the 54th Parliament of the United Kingdom with an electorate of 40,611,844, having 24,814,623 valid votes.
| Constituency | Electorate | Turnout | Votes | Vote share | Position |
| Aberavon | 50,685 | 59.4% | 3,545 | 11.8% | 3rd |
| Aberconwy | 43,976 | 62.0% | 3,818 | 14.0% | 4th |
| Alyn and Deeside | 59,441 | 59.7% | 1,320 | 3.7% | 4th |
| Arfon | 42,998 | 58.2% | 8,028 | 32.1% | 2nd |
| Blaenau Gwent | 53,301 | 66.1% | 843 | 2.4% | 4th |
| Brecon and Radnorshire | 55,171 | 69.5% | 1,404 | 3.7% | 4th |
| Bridgend | 57,046 | 59.7% | 2,350 | 6.9% | 4th |
| Caerphilly | 64,120 | 56.5% | 6,565 | 18.1% | 2nd |
| Cardiff Central | 61,079 | 59.2% | 1,271 | 3.5% | 4th |
| Cardiff North | 64,390 | 70.4% | 1,936 | 4.3% | 4th |
| Cardiff South and Penarth | 67,855 | 58.2% | 2,071 | 5.2% | 4th |
| Cardiff West | 64,587 | 58.2% | 4,855 | 12.9% | 4th |
| Carmarthen East and Dinefwr | 52,741 | 70.8% | 17,124 | 45.9% | 1st |
| Carmarthen West and South Pembrokeshire | 57,143 | 67.3% | 5,960 | 15.5% | 3rd |
| Ceredigion | 52,514 | 68.0% | 12,827 | 35.9% | 2nd |
| Clwyd South | 51,201 | 61.2% | 2,958 | 9.4% | 4th |
| Clwyd West | 55,381 | 65.1% | 3,912 | 10.9% | 4th |
| Cynon Valley | 48,272 | 60.2% | 3,939 | 13.5% | 2nd |
| Delyn | 53,383 | 63.7% | 2,524 | 7.4% | 4th |
| Dwyfor Meirionnydd | 48,823 | 61.4% | 15,228 | 50.8% | 1st |
| Gower | 60,432 | 65.4% | 3,089 | 7.8% | 4th |
| Islwyn | 56,225 | 60.2% | 4,213 | 12.4% | 2nd |
| Llanelli | 55,280 | 63.9% | 9,358 | 26.5% | 2nd |
| Merthyr Tydfil and Rhymney | 54,044 | 55.5% | 2,972 | 9.9% | 3rd |
| Monmouth | 62,233 | 73.4% | 993 | 2.2% | 4th |
| Montgomeryshire | 46,655 | 66.3% | 2,156 | 7.0% | 4th |
| Neath | 57,278 | 62.5% | 6,125 | 17.1% | 2nd |
| Newport East | 54,941 | 57.9% | 1,221 | 3.8% | 4th |
| Newport West | 60,303 | 59.3% | 1,278 | 3.6% | 4th |
| Ogmore | 53,842 | 59.5% | 3,274 | 10.2% | 4th |
| Pontypridd | 54,122 | 63.2% | 3,757 | 11.0% | 4th |
| Preseli Pembrokeshire | 56,001 | 70.0% | 4,895 | 12.5% | 4th |
| Rhondda | 50,461 | 61.7% | 4,956 | 15.9% | 2nd |
| Swansea East | 57,502 | 53.6% | 2,129 | 6.9% | 4th |
| Swansea West | 58,363 | 56.7% | 2,150 | 6.5% | 4th |
| Torfaen | 60,665 | 59.3% | 2,242 | 6.2% | 4th |
| Vale of Clwyd | 49,637 | 65.8% | 2,346 | 7.2% | 4th |
| Vale of Glamorgan | 68,229 | 68.5% | 2,426 | 5.2% | 4th |
| Wrexham | 48,016 | 63.3% | 1,744 | 5.7% | 4th |
| Ynys Môn | 52,512 | 67.5% | 11,036 | 31.1% | 2nd |
Turnout as calculated by the House of Commons Library, is the total number of votes cast and not spoiled, divided by the size of the electorate.
Under section 13(b) of the Representation of the People Act 1985, a candidate gaining 5% or less of the vote share will forfeit their deposit.
Estimates of the 2005 general election result in new constituencies
Colin Rallings and Michael Thrasher, then at the University of Plymouth, produced estimates of the 2005 general election result as if the new constituencies recommended by the separate Parliamentary Boundary Commissions for England, Wales and Northern Ireland had then been in existence.
The Elections Centre, established by Professors Colin Rallings and Michael Thrasher, moved to the University of Exeter in 2003.