Alberto: Broadly speaking, younger people and households with higher social grades and levels of education tend to support Remain in greater numbers. Older people and those on lower social grades and education lean for Leave.
The two official campaigns, one for each side, are called Vote Leave and Britain Stronger in Europe. But they are not alone in making the respective cases. The Conservative government’s official position is for remaining in the EU, but the party itself is split on the issue, with several prominent Tories, Boris Johnson above all, backing Brexit. Most of the Labour party supports staying in, even though party leader Jeremy Corbyn says there is a lot he wants to change about the EU.
UKIP wants Britain to leave the EU. The SNP, Plaid Cymru, the Lib Dems, and most of the Greens want to remain.
I won't bore you with everyone else, except to say that basically every international organization, and most foreign leaders, want us to stay in the EU. They really don't like uncertainty.