This is an important point. You've got the government talking about regional pay because of the disparities across the country, yet it appears this income threshold will be uniform. To show how absurd this is: consider london weighting. It brings my income up to circa 25k a year. Yet someone doing the same job up north somewhere gets around 18k. Now, with income from other areas (including overtime, if that will be considered) I might squeeze over a possible 25,700 threshold but the person earning 18k will be denied. And here is the rub: it isn't that good a wage in London! Mainly because of housing and transport costs. You'd probably be better off on the 18k up north. In the short term at least.
And yes, London is increasingly like a city state. We even have our own executive and mayor. But then, generally, England is very much Balkanised now with major disparities between the different regions.