at lancaster in your first year, you have to take three modules. some major subjects like economics requires you to do two modules and leaves you one free to do another subject of your choice.
if you have previously studied economics you take econ101 and if not you take econ102. as an economics major you also take econ103.
i took economics as my minor last year so only studied econ102 but 101 and 102 are taught the same. half the course is microeconomics and the other half is macroeconomics. in each half you have three tests - a short answer test, an essay test which you are given the questions for in advance, and a multiple choice test. if you pass all tests and get an average on 55% for macro or micro or both you do not have to sit the summer exam.
i don't know much about econ103 but i know that if you have done maths at a-level it will help as there is some differentiation and other calculus in the work.