According to Google it’s Wakefield for cities.
Dudley must be up there, if not the top, for a town though.
Five minutes or so of Googling has told me that Wakefield has a population of 30,000. Or 99,000. Or 329,000. Or 348,000. All as clear as mud. It seems the larger figures are for the local government area, which seems to be called City of Wakefield, and which appears to include Pontefract, Castleford and other such discrete towns. The smaller figures are for Wakefield itself, but I don’t know why different sources vary between 30,000 and 99,000.
So, to sum up…I am not sure, and I feel that I understand less than I did ten minutes ago. 
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Thanks for clarifying that mate 
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Any time. 
I looked here. The problem is that boundaries keep changing. What is a town?
Oh good, the population of Wakefield is 104,000, so that’s a fifth possibility. 
It also depends on the source of the figures and when you are looking them up. We have a UK census every 10 years (last one in 2021). These are tied to a single specific date and are a “best guess” on where you will be on that day (most won’t change but a fraction will due to the unexpected). There is a high return rate as it is a legal responsibility to do so, but not everyone does (especially those with something to hide). So we have fgures for a partucular date with a fairly high rate of accuracy but not 100%. However, the results take a while to collate so by the time they get published they might already be out of date - and get progressively more so over the 10 years until the next one (getting worse with each successive census exercise as the rate of social change and mobility accelerates).
More frequent checks are things like the electoral roll but these aren’t as in-depth and not a legal requirement to respind so lower return rates.
Councils will also make ad hoc guesstimates on things like school enrolment figures, benefit claims, council tax, etc.
As has already been pointed out, it also depends on what boundary you are taking into account (and these are constantly being redefined).Are we talking town, borough, local authority, metropolitan area, catchment area, etc?
The best you can do is try and compare like with like if you can - and keep in mind that the accuracy was never 100% to start with and will drop over time.
Similar to Milton Keynes which includes the towns of Stony Stratford, Newport Pagnell, Wolverton and Bletchley.