OP
oldtimer
Whilst I will agree in principle, that everyone irrespective of whether they are PAYE or self employed are responsible for paying the correct amount of tax.
If a person's employer or contractor makes the deduction, and then doesen't pay it, it is not your responsibility.
Thats fine if you can prove it but the OP was concerned enough to ask the question and as been said if you dont have the documentation then the IR want the money from you