Plough Monday traditionally is the Monday after Epiphany when The Magi visited the infant Jesus. It is the day for putting Christmas and its excess behind us and "putting one's hand to the plough"; in other words, back to work.
It has always been an important ritual of agricultural workers, especially in the east of England where although the plough boys were supposed to return to work they actually paraded the plough through the streets hoping for money from wealthy landowners. It was a cold and barren time of year.
Further Information
In Cambridgeshire in the Ramsey area there are still celebrations (although they may have been moved to Saturdays) featuring traditional straw bears and Molly Dancers. To find out more try www.ourworldfestivals.com or http://www.strawbear.org.uk/