Doesnt even need to be a specimen jar, I did it in a travel shampoo bottle. As long as it totally clean before hand or they think you've been drinking shampoo :-)
You can get them from the surgery, we did just last week, for a specimen from our daughter. of course, i'm assuming that its standard practice all over, would have thought so, failing that, the above posts are good.
Yes you can take it anything but I wouldn't recommend a small whisky bottle, my mum's friend did that and it was stolen from the basket of her bicycle .. doesn't bear thinking about !!!!