Hello and welcome to the site. Thank you for your question.
If your second job does not pay you holiday pay/sick pay etc then factors to be considered in the final decision are
As self employed -
You already pay Class 2 NI contributions £140.40 pa- these would cease and in its place you would pay Class 1 NI.
Additionally, you pay Class 4 NI based on profits in excess of £7,755 from self employment. If your profits are say £9,000 then Class 4 NI would be 1,245 x 9% = £112.05.
There would be savings on NI contribution if you were an employee.
I am not sure what expenses you have been able to deduct from your self employed income in arriving at profits but the scope for expenses is limited when you are an employee.
On the whole, there is little to choose between the two based on level of earnings etc.
You have to decide which option offers more security and continuity of regular second income.
I hope this is helpful and answers your question.
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