UK music filesharing laws: Does my sister have to pay this apparant £375 fine?

Just some quick context:

http://www.zeropaid.com/news/89957/ministry-of-sound-legally-threatens-2000-alleged-file-sharers/

My sister happened to download this album and got a letter sent asking her to pay them £375 or face having to pay hefty fines in court. Is this thing legal, and does she have to pay?

According to the article people have just ignored them and there hasn’t been any action faced.

I am merely looking out for my sister and helping her avoid losing 2 months of wage to this if it can be avoided.

Thanks.