P45 with initial employer

Hi, I have been on the NHS Staff Bank (zero hour contract) for a number of years but they outsourced all of us to NHS Professionals (NHSP). I now work 100% for NHSP but I haven't officially resigned from the NHS who still hold my P45. NHSP are my Primary Employer. Does the fact that the NHS still hold my P45 affect how much tax I pay? I know it seem like a daft question but I technically have two employers. I got paid my first full month from NHSP and I got clobbered for over 30% tax. I'm being told it will even out over the next month or so. Any thoughts?

Hi Andrew,
If you have 2 employments, and your now secondary employment was previously your primary, this could affect the allocation of your allowances.
You can use the following link to check your tax code/s is/are correct.
How-to-update-your-tax-code.
If you are unable to resolve your query this way, please contact HMRC to check your tax codes.
Income Tax: general enquiries
​​​​​​​Thank you.