So, how do you get to India from the UK? Well, the are any number of subtleties but broadly the problem you face is avoiding Afghanistan. Whilst it's not as bad as it was [1] you and me are unlikely to include it on the itinerary.

To avoid Afghanistan, if you look at a map, you must either go over the top or underneath.

The problems for all the countries you're looking at traveling through are the same: paperwork. Does it have to be done before you arrive at the border or can it be winged when you get there? Having travelled a fair bit I've noticed that many counties that announce loudly that you must do the paperwork in advance are happy to do it on the border when you arrive and often charge less. Maybe it's about minimising the paperwork at the border? Anyway, what you don't want to do is mess up with a critical country. It'd be a real pain to be turned back at the Pakistan border but you might just shrug your shoulders at the Bangladesh border.

The paperwork isn't just about a visa. You're taking a vehicle into the country and that requires a carnet, whether temporary or otherwise. The carnet is basically a promise not to dump your vehicle in their country.

Green cards only work in Western Europe so you'll be buying third party insurance wherever you go. Don't worry, they're all set up to take your hard currency off you.