http://www.hmrc.gov.uk/cnr/p85.pdf
This is the form that you fill in to claim income tax back. This will be calculated on your earnings from the 6th April, as if it is your total earnings in the year.
If you have been paid by PAYE and have not worked the full 12 months, there is a high chance you will get some tax back, as the tax deducted from your / weekly payments is calculated as if you were working for the full 12 months by for example splitting the tax free personal allowance over the 12 months.