I thought Kenilworth was larger, and Wikipedia confirms this, though not by much - 22k compared to 19k in 2011. I hadn't realised Melksham had grown that large. Perhaps due to the station?
This is where you need to be very careful what you are comparing, and work out which figures to use when you're looking at facility provision - be it station, shops or sewage. And also look at time scales - last year, this year, next year, sometime, never.
The population of the City of London is around 9,000 ... but then The City is the "Square Mile" is the the historic centre and the primary central business district. People work there and don't reside there. Melksham has a similar but far less extreme division - Melksham Town with 19,000 in the 2011 census. But then "The Parish of Melksham Without is in the Melksham Community Area. It surrounds the Town of Melksham and has a population of approximately 7,500." And with a growth of the built up area, you can walk down a street and go from one to the other without seeing any border. To complicate calculations, a significant number of residences that were built in Melksham Without can only be reached by road from the Town, and the whole thing got so absurd that a number of chunks of the without were moved within a couple of years back.
Treat the current population as being 27,000 rising by about 10,000 in the next 10 years. And, yes, I can point out the sites where housing is being built or are earmarked. A neighbourhood plan video (in which, regrettably, I appeared), co-ordinated by both Town and Parish will be out in a couple of months. It suggests safeguarding an eastern bypass route, building housing areas which are transport friendly and porous to allow buses, self drive pods, cyclists and walkers cohesive community connection, and protecting land at the station and on the routes to it to ensure good and continued transport hub development there.
Off topic - feel a split coming on, unless someone can add a good Kenilworth comparator. I suspect that with "without" they are much more similar than a casual reader might have guessed, and in other aspects other than raw population too.