Union is what schools play, and is associated with the South of England. It's spiritual home is Twickenham. There are 15 players and they can spend a fair bit of time in the scrum - when they form a huggy huddle
. If those working in the City of London or Home Counties say rugby, this is what they mean.
It used to be that some players would go from being amateurs (Union) to putting in a few years in League (paid) at the end of their careers to make some cash, because once you went professional you couldn't swap back to amateur again. England Rugby union players were often lawyers (Brian Moore) or doctors (can't remember the one that was a surgeon, but I always worried about his hands!). The very good players sometimes 'worked' for their rugby union club in the office, as a way of getting round the pay rules. There was a lot of snobbery about League. Then Rugby Union became professional (paid). The players are now able to move between codes at will.
Now you will see players moving from League into Union eg Jason Robinson who scored England's only try in the 2003 World Cup Final.
League is traditionally Northern and working class - the players were paid as they couldn't afford to give the time for free. There are 13 players, and it is faster moving than Union - though since Union became professional (paid) the play has become faster as the players have become fitter. The team with the ball has 5 goes at getting a score, losing one each time they're tackled. If the other team touch the ball the count restarts. After the fifth tackle, if they don't score or kick the ball away, the ball goes to the other team. Common to both codes, you can't pass or knock the ball forward (except with your feet) or tackle someone above the neck. Once the player has been tackled, the tackler has to let them up to play the ball - you'll hear the ref shout 'Mooooove!' League has also had changes in recent times, moving from being a winter to a summer sport, and acquiring double barrel names eg Leeds became Leeds Rhinos. And League had the Sin Bin before Union - a player given a yellow card has to sit on the naughty step on the designated bench for 10 minutes before being allowed to rejoin play.
Who are you going to see?