Heh, CB beat me to the move
I was going to comment that while I can't speak for your local laws, I would believe it is shaky ground leaving a minor unattended. Legal? I don't think so. Common practice? Yes.
If the kid is mature, and can handle themselves, then you'll probably be alright. However, you have to keep in mind that because they are a miner, and and all issues that arise for them will be your responsibility - meaning if the house burns down, or someone breaks in, or they throw a party and someone gets injured or killed - you, as the legal guardian, are responsible. And if you are away on vacation or whatever, it'll be damn hard to get back home in a hurry should such issues arise.

But that's a risk every parent makes, as a lot of 'latch-key' kids are home alone between getting out of school and when the parents get home from work, or as noted during babysitting, etc. But in these cases, the responsible adult is usually less than an hour away and typically has emergency numbers and contacts available for the kid.
You've got the added wrinkle of a prick of a father watching the situation - and it would be very easy for him to call social services to investigate your absence. I don't think they'd look to kindly on a minor being alone for days or weeks at at time. Hours, perhaps, and the distinction of how long is too long is a very grey one, but I'd ask you if it is worth it to take that risk
I can totally relate to both the kid wanting the independance, and to the parent wanting to trust the kid while away for an extended time, but I'd recommend against it - just my opinion.
Mods may want to move this to SO after it gets a decent Legal run thru, unless there is a fear of SO turning into a parenting lecture...which wasn't the original intent.