CA80600 | Dredging: Pre-trading expenditure and expenditure incurred before premises are occupied
From HM Revenue & Customs · Capital Allowances Manual
Treat capital expenditure incurred on dredging for a qualifying trade before the qualifying trade begins as incurred on the day that the trade begins.
Treat capital expenditure incurred on dredging in connection with a dock or other premises as incurred on the first day on which:
the person both carries on the qualifying trade, and
the dock or other premises are occupied.