I went to Twickenham  4/5  years ago to see the Union vs League game. The first half was played with League rules and the second with Union. The Union side was slaughtered in the first half and I expected a complete reversal in the second. Not a chance the league guys won, not by such a big margin, but they showed the Union guys a thing or two. 
The crowd I went with, all from Beaconsfield Rugby Club, were all die hard Union fans and didn't think much of "Those Northern poofs coming down here to show us their watered down poncy rugby"
There was a lot of huffing and puffing going on during the second half as the League guys were banging in the tries, and even they had to concede that league was a whole lot better than they expected.
I was brought up on Union and have never been to a league game so I am a bit bias. I must try it next time we are oop t north visiting the sister in law. You never know , I might enjoy it.
I must have a google and find out why there are two codes when it started out as one.
I got it 
The schism between union and league
For more details see History of rugby league
It is believed that Yorkshire inaugurated amateurism rules in 1879, their representitives along with Lancashire's, are creditied with formalising the RFU's first amateur rules in 1886. Despite popular belief, these Northern bodies were strong advocates of amateurism, leading numerous crusades against veiled professionalism. However, conflict arose over the controversy regarding broken time, the issue of whether players should receive compensation for injuries received whilst playing. The northern clubs were heavily populated by a working class, and thus, a large pool of players would either not turn out for their clubs due to working commitments, or forgo pay to play rugby. In 1892, allegations of player payments were directed at the Bradford and Leeds clubs, though this was not the first allegation towards these northern bodies, that is not to say southern bodies had not been involved in similar circumstances. The RFU became concerned that these broken time payments were a pathway to professionalism.
On August 29, 1895 at a meeting at the George Hotel, Huddersfield, twenty clubs from Yorkshire, Lancashire and Cheshire decided to resign from the RFU and form the Northern Rugby Football Union which from 1922 would be known as the Rugby Football League. In 1908, eight clubs in Sydney break away from union and form the New South Wales Rugby League. The dispute about payment was one which at the time was also affecting soccer and cricket. Each game had to work out a compromise; Rugby was the least successful at doing this. It would be a century before union legalised payments to players and would allow players who had played a game of league (even at an amateur level) to play in a union game.
Sorry Dave,  Thread well and truly highjacked.