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.