Sorry if this is an obvious question.. I want to slowly acquire the whole ECML route. But I'm so confused which DLC's are needed because there are so many of them. If you can provide links that would be great. Thanks!
You will need for the ECML Merge from Alan Thomson Simulation ATS: ECML: London - Peterborough ECML Modern: York - Peterborough North East England (DPS Simulation) or ECML North East - Both of these have extra requirements but the ECML North East has less needs ECML Newcastle - Edinburgh (Just Trains) Southwestern Mainline (not sure if the new version works for this).
The line from Kings Cross to Edinburgh is covered by four routes. East Coast Main Line London-Peterborough (also included in the Great British Railway Journeys pack which is a bargain even at full price if you're collecting British routes), East Coast Main Line Modern Peterborough-York, East Coast Main Line (which covers York-Newcastle) and ECML North: Newcastle-Edinburgh. Just to confuse matters East Coast Main Line used to be called ECML (North) so be careful if you're looking at third party sellers. Each route represents a different time with the York-Newcastle route being very much the earliest (late '70s/early '80s pre electrification). It's also much to the oldest DLC, one of the oldest there is in fact, and rather crude by current standards. DP Simulation has an updated version which is worth a look and includes lines to Teesside- there's another updated version which looks better and doesn't even include the York-Newcastle DLC as a dependency but it stops at Darlington. Alan Thomson lists a merged ECML route which I have no experience of. Hope this at least steers you in the right direction.