It would be better if you did. For eg there are two types of engineers certificates of compliance with planning- one says they inspected at all stages ( including saw foundation poured) and the other says they didnt see stages but from visual inspection of completed house it's ok. The first is better. In anycase shoddy work can be covered up so it is better to have your engineer check at intervals. Over the next few years I think we are going to see a rise in suits against builders for defective work - walls thrown up during the boom etc.