I recently took on a new employee, who has already have another job with another employer. The salary with the other employer is above the threshold, and the salary with me is under the threshold.
You need to give your new employee a form P46 to fill in. From the information you have given in your post your new employee would tick box C indicating they have another job. Ticking box C means you have to apply tax code BR. When you have filed the P46 with HMRC they will inform you of any other tax code changes.
There are two options (there are probably more but I have quite a simple mind so two options is enough for me).
Either the entire tax code is used in the first job where they receive relief and they are taxed in everything in your employment.
Or
HMRC issue two seperate tax codes, one for each job.
Have HMRC been informed already that you have taken the new employee on?
kind regards,
Shaun.
__________________
Shaun
Responses are not meant as a substitute for professional advice. Answers are intended as outline only the advice of a qualified professional with access to all relevant information should be sought before acting on any response given.
Incidentally NI is a tax on employment, and as such is charged separately and independently on each employment as if the other employment didn't exist (except in certain rare circumstances involving high earners). So this employee will be charged NI as if this were their only job.