Ground hardness
Firm clay, compacted fill or gravel can increase the base rate by 25–50% through slower digging and additional hand tools.
Depth
Excavation below 1.5 m commonly adds 15–35% where lifting, access and safe working become more onerous.
Restricted access
Confined working areas, low headroom or long barrow routes can increase rates by 30–70%.
Existing services
Careful excavation around live or suspected services typically adds 20–50% for reduced productivity and supervision.
Water and instability
Local pumping, soft formation and repeated face collapse can add £40–£120/m³ before any formal temporary works.
Quantity and continuity
Small isolated excavations may carry a 30–60% premium because mobilisation, supervision and downtime are spread over limited volume.