Hs2 - destroy huge swathes of the country to get workers into London Open immigration policy only so London can get cheap workers in. Rest of country don't need (or want) mass immigration. Ever increasing population to keep workers "in their place". Leftie liberal London centric politicians don't know or care what the rest of the country wants
I think that as an American, the argument that the rest of the United Kingdom would be better off without London is very much a parallel to what happens here in the USA. One could argue that the United States would be better off as a whole with California gone.
London is a vital part to the history of the United Kingdom and was instrumental in its development to where it is today, for better or worse. To deny London being a part of the United Kingdom would be to deny the United Kingdom itself. To many, London is the United Kingdom, even if it is not true, it is still a large part of its history.
The per capita income of the London metropolitan area is much higher than that for the rest of the UK. Much of the tax revenue collect to the royal purse comes from the economic activity in London. It would cost each household in the rest of the UK thousands of pounds in additional tax for programs like the National Health and Defence, which are now shared by London.
When people think of the United Kingdom, the first place they tend to think about is London. It is a major part of their history. It is also the capital and the largest city in the United Kingdom. It is essential for the UK economy to have London rather than not.