From the HMRC site, it seems I might be able to claim back once I finish working (rather than waiting til April).
http://www.hmrc.gov.uk/incometax/stop-work-refund.htm
If you’re unemployed for at least four weeks or you retire or return to studies
If you think you’ve paid too much tax, you’ll need to claim a tax refund from HMRC if any of the following applies:
•you’ve been unemployed for at least four weeks
•you stopped working because you’ve retired and you’re not getting a pension from your old employer
•you’ve returned to studying
You can claim a tax refund by filling in form P50 Claiming tax back when you have stopped working. Send this to HMRC, together with form P45, Parts 2 and 3 – and keep Part 1A for your own records.
HMRC will send you any tax refund you’re entitled to by post. They’ll also send you a new form P45, Parts 1A, 2 and 3, if necessary.
If you retire and get a pension from your old employer, you’ll get back any refund you’re entitled to with your pension payments. You won’t need to claim a tax refund using form P50.
If you were made redundant contact HMRC before filling in form P50 and they will tell you what other information you need to provide.