Ideally, but on a two track railway, like the ECML that you mention, there's no room for one train to stop at all of the stations you've not mentioned (Grantham, Newark, Retford, Doncaster, Durham, Morpeth, Alnmouth, Berwick, Dunbar etc) since it'll stop anything "fast" from running non stop services from London to York etc at any "fast" speed
You can run a lot more "semi fast" services per hour than trying to have some "fast" and some "slow" services (or you do what BR did on a number of lines and close lots of smaller stations, of course)