What factors influence the frequency of by-elections, and are some councils more prone than others to having to fill casual vacancies?
And how should we go about answering this question when there is great variation in council size? Richmondshire, for example, has just 24 councillors but Durham has 126. It is reasonable to assume that larger councils will have more by-elections than smaller ones.
The frequency of May elections, too, must have an impact. In normal circumstances, a by-election will be held over if a May election is scheduled within six months of the vacancy. Councils with elections by thirds have more scope to avoid by-elections than do those authorities electing members every four years.
Most by-elections occur either because of resignation, accounting for almost 60 per cent of cases, or sadly, death, which explains over a third of by-elections. When a councillor dies, local parties have little choice over when the election is called.
Resignations are another matter. Incumbent parties may exercise some control over when their colleague resigns, thereby increasing the chance of holding the seat. Of course, when there is acrimony, a resigning councillor may choose the most inappropriate moment.
This is not to say that councils with frequent by-elections are necessarily less stable than those that hold fewer contests, since councillors that defect to other parties are not obliged to fight a by-election.
Examining the frequency of by-elections held since 1983 confirms May as the most popular month – 15 per cent of all vacant seats are contested then. This is an under-estimate since our practice has been to incorporate double vacancies into the overall results rather than to treat the scheduled election separately from the casual vacancy. The May totals vary according to the election calendar, peaking in years with county council elections as councillors on the lower tier districts use the election to stand down.
June and July are also popular. Together, these three months account for 36 per cent of all by-elections. There is another surge between September and November when another third of contests happen. From December through to February, however, quietness descends on the electoral landscape, with only 16 per cent of contests occurring then.
Followers of by-election results will know some councils appear regularly. Eight councils have had 50 or more of these contests since 1983. Top spot is shared between Hackney and Lancaster, each with 56 by-elections. But both authorities have reasonably large councils elected every fourth year so cannot often take advantage of the six-month rule.
Comparing the relative frequency of by-elections means taking account of both council size and electoral procedure.
Hackney, for example, falls to third place after measuring the number of by-elections as a ratio of total council seats. This approach has become familiar during the Covid-19 crisis, when the number of confirmed cases per 100,000 population is reported for each local authority area.
Here, we measure the by-election rate per 10 council seats. Because council size may vary over time due to boundary and structural changes, the median value is used.
Hackney’s rate is 9.3 by-elections per 10 council seats while Lancaster’s is 8.7, placing it seventh overall.
The overall list is headed by Boston with 33 by-elections recorded. A median council size of 32 seats produces a score of 10.3. Interestingly, neighbouring North Kesteven lies second on 9.5, after registering a total of 38 by-elections.
Boston’s familiarity with by-elections mostly reflects its turbulent local politics. During the 1990s, there were skirmishes between Conservatives and Independents. This later developed into clashes with the Boston Independents, and more recently UKIP became a force in Boston’s elections. Many vacancies followed resignation of the sitting member.
A significant fraction of Independent councillors in North Kesteven may have contributed to its position in the by-election league table. The authority has had 10 by-elections in the past five years, most of which have seen the Lincolnshire Independents either winning or losing seats.
The data show that councils voting every fourth year are more likely to have more frequent by-elections. It is safer to control for this factor and compare authorities that share methods for determining council seats.
In London, the range for council size lies between 50 and 70 seats and all seats are determined at a single election every fourth year. After Hackney, the league table features Lewisham (54 by-elections; 8.1 cases per 10 seats), Haringey (42, 7.1), Camden (40, 6.8) and Tower Hamlets (40, 6.8).
The fewest number of by-elections is Wandsworth which has had just 17, a ratio of 2.8. A larger than expected fraction of these cases appear to be the result of councillors dying in post rather than resigning. Hillingdon (3.2) and Waltham Forest (3.3) are other boroughs where few casual vacancies have occurred.
Among the metropolitan boroughs, there is a much greater variation in council size than is found in London. Birmingham’s median council over this period is 117 seats while Bury’s is just 48 seats. Comparisons of ratios is better in these circumstances although these boroughs no longer share the same electoral method, with three now using a four-year cycle.
Among this class of authorities, it is Calderdale that has the highest ratio of 6.5. Its West Yorkshire neighbour, Kirklees (4.9), is in third place with Newcastle upon Tyne separating them with a score of 5.0.
By contrast, Gateshead has the lowest ratio of by-elections; its 13 cases produce a ratio of just 2.0 with Sunderland (2.4) and South Tyneside (2.7) occupying the next places.
The average ratio in the metropolitan authorities is 3.5 with London boroughs averaging 5.1. This is largely because of the different electoral methods being used.
Since Welsh local government reorganisation in the mid-1990s, councils have all moved to a four-year cycle. In the quarter century since then only 337 by-elections have been recorded. Although Conwy (4.7) and Gwynedd (3.7) have the highest by-election/ council size ratio, the scores generally are lower than in England.
The lowest incidence of by-elections is found in Blaenau Gwent, which has held just seven since 1996, the majority of which followed the sitting member’s death.