CH155506 | Penalties for failure to pay on time: rules for specific taxes: Soft Drinks Industry Levy (SDIL): penalties - failure to pay all or part of amounts due – overview

From HM Revenue & Customs · Compliance Handbook

If a person fails to make a full payment of SDIL by the due date, they become liable to a penalty on the amount unpaid.

The penalties for failing to pay SDIL in full and on time are

an initial penalty of 5% for SDIL unpaid at the penalty date, see CH155507, and
two further penalties of 5% each for SDIL unpaid at 5 and 11 months after the penalty date, see CH155508.

So a failure to pay that continues for 11 months after the penalty date can incur all of these penalties on the same unpaid SDIL.

It is important to distinguish between

the due date - the date when the person needs to pay the SDIL, and
the penalty date - which is normally the day after the due date and the first date on which a penalty is chargeable for a tax period.

FA17/Section 52