The typical number of votes you need to be elected is somewhere around 8,000 to 10,000, so a constituency would probably have about 60,000 electors, I think. They're actually set on the parameters of population. The constitution says it should be a certain ratio of MPs to population, so that's about the size of them. For each MP, there are relatively few voters. That's not necessarily a feature of the system; it's just how it works here.
On July 26th, 2016. See this statement in context.