Photo credit: http://www.anglican-mainstream.net/2011/04/15/st-george-gets-his-bank-holiday/
Cut and pasted from Wikipedia:
St George's Day in England
Saint George is the patron saint of England and as such is celebrated on his death each 23 April. This is also celebrated as the day of birth and death of William Shakespeare. For this reason, the 23rd of April is celebrated as "Shakespeare Day".
St George and the Dragon
According to the Golden Legend, the narrative episode of Saint George and the Dragon took place in a place he called "Silene", in Libya; the Golden Legend is the first to place this legend in Libya as a sufficiently exotic locale, where a dragon might be imagined. In the tenth-century Georgian narrative, the place is the fictional city of Lasia, and it is the godless Emperor who is Selinus.
The town had a pond, as large as a lake, where a plague-bearing dragon dwelled that envenomed all the countryside. To appease the dragon, the people of Silene used to feed it two sheep every day, and when the sheep failed, they fed it their children, chosen by lottery. It happened that the lot fell on the king's daughter, who is in some versions of the story called Sabra. The king, distraught with grief, told the people they could have all his gold and silver and half of his kingdom if his daughter were spared; the people refused. The daughter was sent out to the lake, decked out as a bride, to be fed to the dragon.
Saint George by chance rode past the lake. The princess, trembling, sought to send him away, but George vowed to remain. The dragon reared out of the lake while they were conversing. Saint George fortified himself with the Sign of the Cross, charged it on horseback with his lance, and gave it a grievous wound. He then called to the princess to throw him her girdle, and he put it around the dragon's neck. When she did so, the dragon followed the girl like a meek beast on a leash.
The princess and Saint George led the dragon back to the city of Silene, where it terrified the people at its approach. But Saint George called out to them, saying that if they consented to become Christians and be baptised, he would slay the dragon before them. The king and the people of Silene converted to Christianity, George slew the dragon, and the body was carted out of the city on four ox-carts. "Fifteen thousand men baptized, without women and children." On the site where the dragon died, the king built a church to the Blessed Virgin Mary and Saint George, and from its altar a spring arose whose waters cured all disease.
St. George and the Dragon, Edward Burne-Jones
Photo credit: http://www.illusionsgallery.com/St-George-Burne-Jones.html
Modern celebration of St George's day in England
In recent years the popularity of St George's Day appears to be increasing gradually. In early 2009 Mayor of London Boris Johnson spearheaded a campaign to encourage the celebration of St George's Day. Today St George's day may be celebrated with anything English from morris dancing to a Punch and Judy show. In 2011, a campaign to make St. George's Day a public holiday in England began on the UK government's e-petition website. If 100,000 signatures are obtained before the deadline in August 2012, the matter will be opened for debate in the House of Commons.
A traditional custom on St George's day is to wear a red rose in one's lapel, though this is no longer widely practised. Another custom is to fly or adorn the St George's Cross flag in some way: pubs in particular can be seen on 23 April festooned with garlands of St George's crosses. It is customary for the hymn "Jerusalem" to be sung in cathedrals, churches and chapels on St George's Day, or on the Sunday closest to it. Traditional English foods and drink (e.g. afternoon tea) may be consumed.
There is a growing reaction to the recent indifference to St George's Day. Organizations such as English Heritage, and the Royal Society of Saint George (a non-political English national society founded in 1894) have been encouraging celebrations. There have also been calls from some commentators to replace St George as patron saint of England, on claims that he was an obscure figure who had no direct connection with the country. However there is no obvious consensus as to whom to replace him with.