Having full time job but working extra for agency

I’m employed full time but it’s coming up to our quiet time and while I enjoy the extra time at home I can’t really afford to lose any money at the moment,
An agency local to me can pay a very good rate for Saturday and I’m thinking of doing the odd shift,
My concerns are will this complicate my tax from my main job and how do I register for tax?? as I won’t have my p45
Hope some of you can advise me,
Many thanks

You’ll just pay emergency tax on the agency work, which I suspect would be correct anyway.

No need to register for anything. No P45/P46 and the agencies payroll will automatically have your tax code as ‘BR’ (Basic Rate).

Fill in a P46 when you sign up with them ticking the box that states you already have a job.

If you’re earning at least £221.15 a week in your main job you’ll not be overpaying any tax in any week you do agency work as well as you’ll have already used the full tax free weekly allowance in your main job. If you do end up overpaying you can claim the overpaid tax at the end of the year online.

Don’t for get to tell the people you work full time for