Of course you can learn the basic things on a keyboard and play some beautifull pieces but you won't get to grade 8 I think 
Sure you can, in fact the difficult things like speed are much easier on a keyboard where the keys will fall if you sneeze too hard. But most keyboards I've seen are short a few octaves, which will put a good chunk of repertoire out-of-bounds. All of Bach's keyboard music will fit into a keybaords range...
The problem is that after learning on a keyboard, everthing will have to be adapted to weighted keys once you get on a real piano, which is quite the adjustment.
I would recommend a good digital piano, with weighted keys. It's cheaper than a real piano, can be played through headphones (incredibly useful when you don't want to disturb the household!), no maintainance and portable. Because of being able to practice through headphones, you will want to keep the digital piano even after you get ahold of a real piano.
The keyboard is good if it's all you got, but you should try and get onto something with weighted keys and better sound quality ASAP. I'm sure if you try hard enough you'll find a way to afford it.