Here's how I setup Fallout 4 / Fallout London

Did a clean install of Fallout 4 GOTY via the GoG offline installer, then launched it ONCE.

Installed Fallout London via the GoG offline installer, then installed it proper by launching the Fallout London "executable" shortcut (You need to double install it, seriously?)

Installed Buffout 4/xSE Plugin Preloader/Address Library (don't forget the vis redist dependencies) and
also High FPS Physics Fix because Bugthesda still hasn't fixed long load times and neither has Team Folon (remember to configure the High FPS Physics Fix cfg file to your liking).

Remember to install these addons to the proper folders within the Fallout 4 GOTY folder, and not the Fallout London folder, because apparently that folder is just for installing the game. You can delete the Fallout London folder after (actually) installing it, I think.

Configured graphics settings (via the regular Fallout 4 launcher settings) to High preset, then set Shadows to Medium (because they're badly optimized), and turned Reflections and Motion Blur off.

All of this has reduced crashing by about 70%, and the game usually runs well.

Feel free to make a shortcut to f4se_loader in the Fallout 4 GOTY folder, since that is what is used to launch the game with the script extender, which Fallout London uses by default. You're going to need to make a shortcut to that if you delete the Fallout London installation folder after installing it.

Same crash here, after boarding the train, fade to black, Fallout London neon logo, then loading screen -> BSOD
Clean install like described. Sad, but I think this total conversion mod needs still some time yet.

I don't blame anyone. I donated some money to the dev's instead. Maybe that helps a bit.

I've ran in to this same issue.
Installing Buffout and its xSE Plugin Preloader dependency, did nothing.
Changing the resolution and going to "windowed mode", did nothing.
What did work was rebooting my system.
This might be a cache error.

I was able to load the auto safe right before the Tube train and play to the Logo page. It then loaded the next area without issue.

I installed Fallout and London fresh from the store and played, had the same issue as the original poster, crashed after/before the train and while on the walk with the vagabonds.

Uninstalled both fallout and London in frustration.

For what it's worth, I reinstalled fallout via GOG and played it till I left the vault and met Codsworth.

I then quit out and decided to install Fallout London via GOG. For what ever reason London now works and has not crashed? No mods or extra downloads used and I launch the game via GOG Galaxy. Give it a try, maybe playing Fallout sets up the base game some how?