England, Scotland, Wales and Northern Ireland are the countries that make up the UK. In your KS3 Geography lessons, you will (hopefully) have been taught that the UK does NOT include the Republic of Ireland! There is sometimes talk on the TV about the north/south divide of the UK. People from London say that anything north of Watford is the north but people in Liverpool say that the south begins at the River Mersey. Geographers are a little clearer about it, they say that it is a line that divides upland from lowland and marks the change from mainly arable to mainly pastoral farming. In geographical terms, it is a (slightly wiggly) line from the mouth of the River Humber to the start of the Severn Estuary.
In terms of human geography, the south fares better than the north - a slightly better life expectancy, higher income, better employment opportunities and so on. Some geographers argue that the dividing line should carry on south to the River Exe, making most of Devon and Cornwall part of the 'north'. It is probably better to think of this as more of a north and west/south and east divide.