I agree with Glenn’s comments about poor drafting, especially the fact that the Sectional Completion Date and Completion Date are the same, which doesn’t correctly apply the principle and intent of a Sectional Completion Date.
Normally you would apply Delay Damages according to what date was ‘missed’, which could be a Sectional Completion Date or ‘the whole of the works’ for the Completion Date. The fact that both are the same day means, that as Glenn says, you are likely to be applying Delay Damages which could amount to ‘double accounting’, that is paying twice for the same assessment.
In this instance, however, it seems that Delay Damages for Sectional Completion have taken account of the ‘double accounting’ principle and, consequently, you would apply Delay Damages to whatever dates are missed, that is BOTH for the Sectional Completion Date AND the Completion Date. If, however, as Glenn states, the Delay Damages for Sectional Completion were £3,000 per day then you could probably challenge the application from a ‘double accounting’ principle.