Unfortunately there is no separate treatment for negative margin or scrap sales.. Standard VAT needs to be applied on sale value unless it qualifies as a zero rated supply

was hoping to come across something under sake of scrap.

As long as the sale is not to a related entity which is not able to recover 100% VAT, the valuation aspect should not get triggered. Thus, you may be able to sell goods at distress value. VAT will be applicable on value of distress sale amount.