My problem is that I am applying to do History&English at some places, and History&politics at others. I don't quite know how to write a personal statement for them both without being too vague. Any ideas?

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I think you really have two choices - 1 focus just on one subject (History in your case) or 2 focus on the common elements between the courses. What ever menthod you use, you will probably want to write a bit about each subject - the amount you write about each one will probably depend on how likely you think you are to get a place and the number of unis you're doing each course at.

There is no real answer to this - it's just a case of balancing your statement so you're likely to get a place at as many courses as possible.