Why are constituency boundaries important?
Well, every constituency is supposed to consist of roughly the same number of electors, so that each elector has as equal influence (as possible) as any elector anywhere else in the UK.
In other words, all votes are (supposed to be) equal – each elector should have equal representation in Parliament.
You can see the size of each constituency in 2005 in Table 10, General Election 2005 Summary of Results. The two extremes show the problem:
Isle of Wight 107,737
Na h-Eileanan an lar (Western Isles) 21,169
It seems that each elector in the Western Isles is ‘worth’ five times more than each elector in the Isle of Wight, given that both constituencies return one MP each.
Of course, some constituencies are more similar in size. Here are two neighbouring constituencies in London:
Chipping Barnet 66,222
Finchley & Golders Green 70,000
So an elector in Chipping Barnet is worth just 5% more than an elector in Finchley & Golders Green.
There is an interesting article in today’s Times about why the boundaries have to be changed from time to time.
When the current parliamentary boundaries were introduced in 1997, one in six constituencies differed by 10 per cent or more from the agreed quota or average number of voters per seat. A decade on, the discrepancy is even larger.
This contrasts with New Zealand and Canada, where a 5 per cent limit is observed, and 3.5 per cent in Australia.
This is apart from differences within the United Kingdom: Welsh constituencies have on average a fifth fewer voters than those in England. (The over-representation of Scotland was largely addressed in 2005.)