Clause 5 deals with cases where goods imported into the UK are either not presented or not declared to HMRC. Where that is the case, it provides for the goods to be liable for forfeiture. It is essential to have rules that cater for situations in which someone fails to meet their obligations when they import goods into the UK. The clause provides such a rule: it makes imported goods liable to forfeiture if they have not been presented or declared to HMRC. That simply mirrors the existing position in EU law that applies in such cases.
The clause also makes it clear that such goods remain liable to import duty at the same time that they are liable to forfeiture. It is essential that appropriate sanctions are in place to deal with failure to meet the requirements of the import duty regime. That is what clause 5 provides in cases where goods are not present or declared to HMRC.