What the report does

For each party in each place, compare how its vote share moved between its two most recent comparable contests with how it moved across the wider area at the same time. The difference — the differential swing — separates genuine local strength from the national tide. Repeated in the same direction at consecutive elections, it marks a place or a person who reliably runs their own race.

How it's built

1. 1

   Pair up comparable contests

   Each ward, council or candidate is compared only against its own last comparable round, with at least 70% of the same wards in play.

2. 2

   Level the seats

   Shares are normalised for changes in how many seats were up, so a two-seat round doesn't look like a collapse next to a one-seat round. Scotland is excluded from this step because it votes by a different system.

3. 3

   Work out the baseline swing

   A ward's baseline is its council's swing; a council's is the mean swing of its comparator group — councils of the same type voting in the same years; a candidate's is their party's swing across their council.

4. 4

   Measure the differential swing

   Actual swing minus baseline swing, in percentage points. Positive is an over-performance against the comparator; negative is an under-performance.

5. 5

   Count the streak

   Where the differential swing repeats in the same direction at consecutive elections, the run is counted so one-off noise can be told apart from a settled local pattern.

6. 6

   Flag what can't be trusted

   Boundary changes, sharp changes in the field, party switches and small comparison groups are flagged and kept out of the headline tables.

How to read it (and how not to)

• • A large gap says a place voted differently from its neighbours. It does not say why — a strong candidate, a local closure, or a party simply not standing all produce the same shape.
• • Wards with a changed boundary between the two contests are compared only where at least 70% of the ward set still matches; the rest are flagged.
• • Candidate scores follow the same person in the same ward. Someone who moves ward cannot be scored, so this understates rather than overstates personal votes.
• • Independents and very small parties swing hard on small numbers, so they dominate the extremes.
• • Scotland's single transferable vote is not comparable with first-past-the-post, so seat-count normalisation is not applied there.