How does First Past the Post work?
First Past the Post (FPTP) is the voting system used to elect MPs to the UK House of Commons.
Each of the 650 Parliamentary constituencies elects one MP.
The candidate who receives the most votes in that constituency wins the seat.
In short
Most votes in the constituency = elected MP.
The winner does not need more than 50% of the vote.
There is no national formula that allocates Commons seats according to each party's total UK vote share.
Why is it called First Past the Post?
The name is an analogy with a race.
There is no actual vote threshold or "post" that a candidate must cross.
The candidate simply needs to finish ahead of every other candidate.
For example:
| Candidate | Vote share |
|---|---|
| A | 36% |
| B | 33% |
| C | 21% |
| D | 10% |
Candidate A wins even though 64% of voters chose somebody else.
What does the voter do?
At a UK Parliamentary general election, a voter normally places one mark next to one constituency candidate.
That vote is counted in the local constituency result.
It is not separately added to a national party ballot for allocating seats.
Why can vote share and seat share be different?
Because the system rewards winning constituencies.
Consider a simplified example with ten constituencies.
Party A wins five seats narrowly and loses five heavily.
Party B wins four seats by huge margins but finishes second in most of the rest.
Party B might receive more votes across all ten seats combined, yet Party A could still win more MPs.
That is not an error in the count.
It is a consequence of a constituency-based plurality system.
What is a plurality?
A plurality means having more votes than any other candidate.
It is different from an absolute majority.
A candidate winning 40% against opponents on 35%, 15% and 10% has a plurality and therefore wins under FPTP.
What are some effects of FPTP?
FPTP can produce:
- a strong relationship between MPs and individual constituencies;
- clear local winners;
- large differences between national vote share and seat share;
- many votes cast for losing candidates;
- safe seats and marginal seats;
- strong incentives for parties to target resources geographically.
It can also produce single-party Commons majorities from much less than 50% of the national vote.
Whether those features are advantages or disadvantages is a matter of political debate.
The factual point is that they flow from the way FPTP counts local winners.
Is FPTP used for every UK election?
No.
Different elections in the UK use different electoral systems.
FPTP is used for UK Parliamentary general elections.
Other electoral systems are used in devolved and some local elections.
The Road to Number 10 simulation is specifically about a UK Parliamentary general election, so its central seat calculation is based on FPTP.
A real example: the 2024 general election
The 2024 result illustrates the difference between national votes and seats.
House of Commons Library analysis records that Reform UK received 14.3% of the UK vote but won about 0.8% of Commons seats, while the Liberal Democrats received 12.2% of votes and won about 11.1% of seats.
The difference arose because of where each party's support was distributed and which candidates finished first in individual constituencies.
This example does not mean FPTP always affects the same parties in the same way.
Its effects depend on the geography and competitiveness of support at each election.
In Road to Number 10
The FPTP Impact section is designed to make this effect visible.
A campaign can raise a party's national vote share without producing an equivalent rise in seats.
Conversely, a smaller national movement concentrated in the right marginal constituencies can deliver a large seat gain.