Scrumpy Jack is a brand of cider made by Bulmers that you can buy in the UK (and, for all I know, elsewhere). It's not 'real' scrumpy, being more of a sanitized, branded, marketing-campaign supported drink.
It tastes noticeably different to the more standard dry ciders available in the UK, such as Strongbow and Dry Blackthorn. It has a distinctly 'farmhouse' aroma to it, which can be quite a surprise on your first sip but becomes quite moreish.
Scrumpy Jack is 6% alcohol, and the remainder seems to be about 80% apples, and 14% pure hangover. You really don't want to be drinking more than two pints of this stuff if you want to enjoy any of the daylight hours the following day. Even hardened cider drinkers will find that Scrumpy Jack can mess you up much more effectively than any of the other common brands.