Do I travel "up" or "down" to London from north of the city?

I am travelling geographically down the country from north of the city of London. Do I state "I am travelling down to London" or do I state "I am travelling up to London" in reference to its capital city status?

In railway parlance an up train would be heading towards London and a down train away from it. So if you were travelling by rail to London, you'd presumably be going up, as it would be absurd to go down to anywhere on the up train.

There are many traditions, with altitude being a pervasive influence (up river / downstream, up in the hills / down to the sea), and latitude also being a common factor, particularly in the UK (oop north / darn sarf [sic]).

Where these traditions conflict, it would be rather zealous to complain about any preference expressed.

Of course, you can avoid any uncertainty by restricting yourself to "I am travelling to London". To my ear, up and down sound more natural when accompanying the verb to go, rather than to travel anyway.

Well technically, up or down have no real meaning in this context, as they do not imply a direction.

The use of the words downtown and uptown, usually refer to the condition of the area, the class of it. In London as a colloquialism, many people say "I'm going down town", meaning going to the city, Westminister, or anywhere within Zone 1 of the underground really. Then again I have heard people use "up to town" meaning London as well.

When there is significant distance involved, it tends to be up in my experience.

Occasionally, though not often, people do think that the difference is akin to heading North (up) and heading South (down); though I believe that is a less common interpretation.

TL;DR: No fixed meaning, you can go up or down to London apparently from anywhere in the country. Preferably try to use compass directions.

It's always up to Oxford or Cambridge wherever you start from. This might indicate that it's up to somewhere impressive or desirable (which London would be to a railway company, at least). Whether the capital is one of those places depends on your view of the country, I suppose.

Also, on many Caribbean islands, 'Above' or 'up along' is on the windward side of the island, usually but not always the west. Not sure if that helps, but it's interesting.