Hi,
You do not report the pension paid under salary sacrifice as no tax relief is due on this. for your own payments, it depends whether they are under net pay or not. Your employer takes the contribution from pay before tax so you get full tax relief whether at the basic, higher or additional rate. No further relief is due.
For earlier years, you would need to claim this separately from your return either by phoning or writing to HMRC.
Income Tax: general enquiries
Thank you.