CA81200 | Dredging: When WDA is due
From HM Revenue & Customs · Capital Allowances Manual
CAA01/S487(1) & (7)
A person can claim a WDA for a chargeable period provided that qualifying expenditure has been incurred and all of the following conditions are satisfied:
during that chargeable period the person is carrying on the qualifying trade for the purposes of which the qualifying expenditure was incurred;
the chargeable period is wholly or partly within the writing down period CA81100;
no balancing allowance is due for that chargeable period.