London's construction supply chain is dominated by a handful of Tier 1 contractors that take on the largest infrastructure and commercial schemes and then sub-package the specialist trades. On the HS2 Old Oak Common station project, the Skanska Costain STRABAG joint venture (SCS JV) is the principal tunnelling and civils contractor, having launched two tunnel boring machines toward Euston in January and March 2026. The station itself will become the UK's largest new rail interchange, and the surrounding 650-acre regeneration zone is already generating demand for groundwork, drainage, concrete frame, M&E and fit-out subcontractors. At Brent Cross Town in the London Borough of Barnet, BAM is on site delivering the first 14-storey office building at what will become an 180-acre, £8 billion mixed-use neighbourhood, with further residential and commercial plots to follow through to 2030 and beyond.
Away from the headline schemes, London's ongoing commercial pipeline keeps a steady stream of Tier 2 and Tier 3 subcontractors employed across roofing, drylining, plastering, joinery and mechanical and electrical work. The data centre construction boom in West London (Park Royal, Slough corridor) and the continued build-to-rent pipeline across East London and the outer zones are the most active sectors in 2025 and 2026. Supply-chain corridors for London typically run along the M25 orbital and the A roads into the city: subcontractors based in Essex, Kent, Surrey and Hertfordshire commute in daily, generating significant mileage claims.
The construction labour market in London is tight by national standards, meaning many subcontractors move between multiple main contractors in a single tax year. That pattern (several CIS300 deduction statements from different contractors) is precisely where errors and missed refunds arise. Many subcontractors on London sites are on the 30% unregistered rate without realising they could have registered for 20%, and some have materials costs deducted at source when they should not be. We audit your deduction statements as the first step in every engagement.