Saint David's Day (Welsh: Dydd Gwyl Dewi Sant) is the feast day of Saint David, the patron saint of Wales, and falls on 1 March each year. The date of March 1st was chosen in remembrance of the death of Saint David on that day in 589, and has been celebrated by followers since then. The date was declared a national day of celebration within Wales in the 18th century.
In 2006 Saint David's Day was officially celebrated on 28 February by Roman Catholics and on 2 March by the Anglican Church in Wales, because 1 March 2006 was Ash Wednesday, which is a day of penitence on which feast days are not celebrated.
A poll conducted for Saint David's Day in 2006 found that 87% of the Welsh wanted it to be a bank holiday, with 65% prepared to sacrifice a different bank holiday to ensure this. A petition in 2007 to make St. David's Day a bank holiday was rejected by the then British Prime Minister, Tony Blair.
(Above taken from here where you can read the rest of the information on St David's Day).