Please resolve a work argument... What are the correct ways in which the above phrases should be used. I don't think they're synonomous (although a colleague does).
I've always used 'up to you' to mean "it's your responsibility" and 'down to you' to mean "it's your fault".
Nowadays, they are used synonymously...eg "It's up to you whether you go or not" and "It's down to you whether you go or not", both simply meaning "the decision is yours". In the past, the 'down' version rather meant it was your responsibility rather than choice..."Team morale will be down to you"...ie one of your functions will be to secure that.
The fact that they are now treated as interchangeable is just an instance of how language changes.
Thank you for your answers...it appears that I am not 100% correct in my office argument, however I'm going to claim I'm right anyway, because none of my colleagues know this site.
What about people who live in the North saying I'm going up to London when it's clearly down! Do people in the South ever say I'm going down to Manchester?! or am I just being picky... I'll leave now...
I think Quizmonster is right: they once had separate meanings but 'down to you' has changed, so they can now be used interchangeably. But I don't think it's set in stone yet, so you could still differentiate the phrases in your own speech without people minsunderstanding you.
I'm with Cider on this one sp, I have always thought that down to you meant you had to do something and up to you meant you had to choose. Another example may help. When you go to buy a car it's up to you which car, when you car needs repairs it's down to you to sort it. I suppose we are splitting hairs a bit but that's how I've always understood and used the phrases.
MORELLO, I think in general people in the North (I take that to mean "north of Watford" and hence to include the Midlands and Scotland as well as Northern England) do indeed refer to "going down to London"; we in the Midlands certainly do. In my experience "up to London" is a Home Counties/West Country expression. Nothing to do with te original question, but there you go.....
lankeela is right regarding trains running to the capital as being UP to London . I used to work for the Post Office and the T.P.O.'s ( travelling post offices ) where always labelled the Up when going towards London and Down when travelling north from the capital . I agree that it does sound strange that going south and up are the same thing - but that was the way the railways wanted it .
FYI, "down to you" is not used in the US
"Up to you" only means "it's your choice"
For the other meaning, we'd say "it will be on your head" or "It will be all your fault" or "it's your funeral" or "you'll answer for it."