It doesn't really have a main cause. Rather a large number of factors came together to make this kind of growth possible.

The Protestant Reformation has more to do than you might think. The Dissolution of the Monasteries opened up considerable land for farming. It also freed up capital and workers, many of the nunneries and friaries were self sufficient but many others produced little more than the spectacle of a relic.

England as a center of Protestantism also experienced significant immigration from oppressed protestants fleeing continental Europe. The Huguenots being the largest group but also groups from other regions.

Mercantilism allowed for increased production through specialization. I know that's a mouthful but let me explain. The increase in shipping of goods allowed people to move to the cities and work in skilled trades such as cobbling. Meanwhile farmer who had previously had to diversify to provide adequate nutrition could now focus on a single crop. An English farmer could grow just barley and trade it for shoes from London and sheep from Ireland.

Additionally mercantilism is allowing the spread of ideas and technology. New casting procedures printing processes paper production all begin or spread significantly during this time.

The Spanish and Portuguese empires were bringing back enormous fortunes from the New World. They were spending this fortune nearly as fast as it came in and that meant flowing capital for most parts of Europe. This provided an incentive to farmers and others to produce as much as possible because they knew they could sell it. Farmers aren't going to produce more than they think they can sell or store this often means fertile land laying fallow.

There are other possible factors too including the rise of banks which could provide capital for building projects. The simple lack of a major plague from 1540-1601. And many others. As I said it doesn't seem to have a single cause.

We shouldn't discount the role of the Black Death. The outbreak in the fourteenth century killed half the population and major outbreaks continued in the fifteenth century killing as much as a fifth of the population in the late fifteenth century. There weren't any major plague outbreaks for much of the 16th century, so based on that alone we should expect a fairly significant increase in population.

Furthermore many historians see the Black Death as instrumental in the breakdown of the medieval world. The Black Death dramatically changed the economic and social relations in England. After the Black Death we see a dramatic increase in wages, agricultural productivity (so food production did increase), and urbanization accompanied with increase in manufacturing. These changes also allow for a greater population.