Need advice about Job

Hi Guys,

Need a bit of advice, i am currently self employed but am thinking of taking a night time job at ASDA just temp over christmas before i say yes to them how will this affect my WTC and CTC and how do i declare this at the end of the year as i would be PAYE with ASDA and Self Assessed for everything else. If there is anybody in the same boat i'd love to hear from you about what you did.

Thanks
Stu