You might be able to claim it back. If you search the HMRC website there's a page about claiming back when you've paid too much tax through your job. It says on there about reclaiming this year (and how to do it for previous years). I looked at it when I was being taxed BR on one of my agencies. I never did it though, they now have a split tax code and I claimed mine back on a Self Assessment Tax return for another job I have.