What was one reason the industrial revolution began in great britain?

 Britain had enjoyed quite a long period of political stability and Britain had been economically prospering. This led to land-owners having spare capital to invest in new ideas and innovations like new machinery. 
The price of agricultural produce had gone up on the Continent, so land-owners could reap great rewards by enclosing their land and buying a seed drill - making many of their farm labourers unemployed. (incidentally this also neutered the only real threat to Britain's stability - the Jacobite pretender - as the highlands were cleared of people to make way for sheep). 
This climate of economic growth, new ideas and innovations (not only in farming, but in science as well), spare capital to invest and an unemployed rural work-force coupled with the abundant and easy to obtain natural raw materials, like coal and iron ore fed the early industrial revolution. 
Another key factor was the British weather - rain to feed the rivers that turned the water-wheels of the early mills and factories.