Having been in the fortunate position of ending supply teaching to take up a part-time post, I decided to contact HMRC about a rebate for overpaid tax in 2011-12 for one of my previous employers, an LEA who last paid me in Dec 2011. Imagine my surprise when HMRC tell me that they can't deal with the rebate yet because I haven't officially been signed off from the LEA, or the agency (I resigned two months ago), or an Academy I worked for in the previous tax year who kept me on their temporary employee list. Be aware that Academies are separate entities to LEAs for tax purposes now, and that agencies may be slow (or useless) in notifying schools of your departure. If you should finish supply work you may have a fair bit of mopping up to do chasing previous employers for P45s - a good starting point is to phone HMRC and ask who they have listed as your employers. Also, if you're fortunate enough to get a long-term supply post, especially in an academy, make sure you get your current tax allowance switched to that employer so you're not automatically taxed at Basic Rate - again, a phone call to HMRC can sort this.