Notional results for a UK general election on 5 May 2005 Elections won 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 | Majority |
| Carmarthen East and Dinefwr | 52,741 | 70.8% | 17,124 | 45.9% | 6,551 |
| Dwyfor Meirionnydd | 48,823 | 61.4% | 15,228 | 50.8% | 8,706 |
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.
Estimates of the 2005 general election result in new constituencies
Professors Colin Rallings and Michael Thrasher, at The Elections Centre of the University of Exeter, 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.