> you are supposed to use trunk roads to navigate to the first town/city on the trunk network beyond where you are going

Yes, this is why it is very useful to know, when navigating out of a UK town / city, the next big town / city beyond your actual destination. If you get on the correct main road, you will usually find signs to your actual destination as you get closer to it. Knowing the main road numbers (A35, etc) as opposed to their names is also really useful as is is the numbers that will be used on the signposts.

So kinda like riding a metro train, where the lines are named after the final destination.

Yes, although the London underground uses a slightly different convention. The lines have names like Northern, Central etc, and most are linear. The line level signage at a station usually directs you to an eastbound / westbound / northbound or southbound platform. The direction and destination of a specific train is indicated by the furthest stop in each direction (which can vary depending on whether the line bifurcates, or a train isn't going all the way to the end).

For example, you'd think about going westbound on the Piccadilly line if you wanted to get to Heathrow from Central London

Eastbound, no? Since Heathrow is West of the center?

Since Heathrow is to the West of the centre, you go westbound to get to it, from the centre.

Sorry, yes, I'm an idiot.

I'm from the UK and was unaware of this method (trunk road to town/city after destination).

Is there somewhere I can read about this in more detail?

Thanks!

Here is a list of primary destinations.

They are separated by region. So for example if you are in Cambridge (EAST region) you follow signs for EAST MIDLANDS. Once you are in that region, you will start seeing signs for the primary destinations in the region.

https://assets.publishing.service.gov.uk/government/uploads/...

It's really just standard manual map based navigation. A dying art these days. I haven't seen many shrubbery related problems, we still have the best signage in the world (that I've seen) and it's perfectly possible to use sign based navigation without any GPS. You however may need to ask directions for the last couple of miles in rural areas.

It used to be documented in the usage section at the beginning of road atlases.