P45

In recruiter context

Three parts. Your previous employer keeps Part 1; you give Parts 2 and 3 to your new employer so they can pick up your tax code correctly. Without a P45, you go onto an emergency tax code (1257L W1/M1 or BR), and you'll likely overpay tax for a few months until HMRC sorts it. You can claim it back, but it's a hassle. Always chase your P45 in your final week — payroll teams are notoriously slow about issuing them, and you need it to start the new role cleanly.