I am entitled to a substantial back payment but haven't received it yet and I am starting work next week, Will I still be entitled to my back payment and how will I receive it?
Your change in circumstances should not have any affect on arrears due to you.
Arrears for a particular scheme are usually paid in the same way that weekly payments were made - so if your money was paid into your bank, the arrears will probably be paid into your account as well.