Once you have made the decision to change employers, there are a few things you need to do to make the change to your next employment easy for tax purposes. Firstly, ensure you receive your P45 from your current employer. On the first day of your new employment, ensure you bring the P45 with you and give to the Payroll department. Your new employer will use the details on your P45 to calculate your tax.
If you do not give your new employer a P45, you may end up paying too much tax because emergency tax may be deducted from your pay.