Can we mix default values and actual data under the UK CBAM?
Partly. HMRC lets you use a default value for a precursor such as billets while using actual data for your own processing. You cannot use actual precursor data with a default value for the finished good. And a return filed with default values cannot later be amended to actual data.
Allowed and not allowed
- Allowed: default value for the precursor, actual verified data for turning it into the final good.
- Allowed: actual data throughout.
- Not allowed: actual data for the precursor and a default value for the final good.
No second chance after a default return
HMRC states that a CBAM return using default values cannot be amended later with actual emissions data. If your figure is likely to be lower than the default, it must be verified before your buyer files, not after.
How it plays out for a rolling mill
A mill whose billet supplier has no verified figure can report the billet at its default and its own rolling at actual data. A mill with verified billet data but no figure for its own rolling must use the default for the finished bar, and the billet data goes unused.
What Senseible does here
Senseible builds actual figures from your own invoices, which is what makes the comparison with the default possible. We build the figure from your records and check every figure in-house; for the UK it must then be verified by a verifier accredited for UK CBAM. Have your own verifier? Send it to them.
Sources: HMRC, UK CBAM iron and steel default values (published 16 October 2026), HMRC, Carbon Border Adjustment Mechanism (CBAM): Policy summary (updated 2 November 2026)
Last reviewed 2026-11-02.