You should actually consider where the data in that Wikipedia article comes from. It's the result of the EU's ESPON project which is a bureaucratic exercise designed to inform the structural regeneration process. At one point that project, when talking about regions, thought it appropriate to lump Ashford (Kent) and Dover with Calais and Lille! If you look at the linked article in more detail it would have us believe that places like Southend, Reading, Basingstoke and Haywards Heath are part of London, that Chesterfield and Doncaster are part of Sheffield and that Macclesfield is part of Manchester. As previously mentioned it lists Chester, Warrington and Wigan as being part of Liverpool, but since Wigan is part of Greater Manchester its population has been double counted. That's not what I would call reliable data and therefore not useful in support of your argument.
From what I have read about ESPON it seems that this data was influenced by travel-to-work patterns but ignores the fact that many so-called dormitory towns supply labour to more than one place and that two-way commuter flows also exist. Bureaucrats in Brussels however are minded to ignore such details in order to simplify their tasks.
ETA: I have just checked the 20 Miles More campaign's report about HS2 to Liverpool and they too have used the same unreliable figures. It's a shame that people campaigning on such a serious issue don't take more care to check their information. The joys of living in a post-truth world I suppose...
