I think a bit of all in one way or another, a better question would be, 'What is the main cause of unemployed during a recession'.
Our value of exported good will fall as interest rates will be cut and hence borrowing will be cheaper, this could actually increase jobs in some sectors.
The value of the pound will fall against the other currencies but then other countries will cut interest rates and hence their currencies will fall also.
The main reason for unemployment though is that banks don't want to lend to each other and hence the public/business, and businesses and consumers go into saving mode. Trying to pay of debt rather than spending. Hence businesses either go bust or they lay of people or just don't employ.
Our value of exported good will fall as interest rates will be cut and hence borrowing will be cheaper, this could actually increase jobs in some sectors.
The value of the pound will fall against the other currencies but then other countries will cut interest rates and hence their currencies will fall also.
The main reason for unemployment though is that banks don't want to lend to each other and hence the public/business, and businesses and consumers go into saving mode. Trying to pay of debt rather than spending. Hence businesses either go bust or they lay of people or just don't employ.

If you think about it in its most basic form, recession = less demand, therefore less demand for goods and services exported from the UK.