You may find that the relevant employment information pre-populates on your return. If it does not, you can contact our taxes department and we can confirm your pay and tax details for 2018/19.
Income Tax: general enquiries
Be aware that you also need your employer's PAYE reference, which is not something we can provide over the phone.
We can send an employment history to you in the post which will show it, but this may not reach you before 31/01.
If you need the PAYE reference you may find it on a payslip, your P45 from your employer, or you could contact them and ask for it.