Inside SIC 71122: The UK's Consulting Engineers, From Giants to Sole Practices

A summary of the Construct365 Sector Intelligence Report on SIC 71122 — the Companies House subclass for engineering-related scientific and technical consulting, home to the UK's consulting engineers. The full report, with the Top 150-derived firm table, the discipline-by-discipline technology audit and the product-fit test, is a free direct download — no email address required.

Disclosure: Section 10 of the report weighs a possible fee-proposal builder for consulting engineers — a Construct365 product idea, currently in development. The report's own verdict is a conditional "maybe, and not now", and this summary presents that verdict with its conditions intact rather than dressed up as a plan.

A barbell market inside one subclass

The wider Consultant Engineering Services group is worth about £80.5bn, growing at a 2.3% five-year CAGR on the strength of the infrastructure pipeline — but the report is careful with that figure: it measures the whole M71.12 group, and the 71122 subclass is a slice of it that published sources cannot cleanly isolate (plausibly £15bn–£25bn, offered as a range, not a finding). What is clean is the population: roughly 32,800 companies are registered to this one subclass.

The shape of that population is a barbell. A dozen or so global giants — AtkinsRéalis at ~£1.5bn of UK fees, Mott MacDonald at ~£1.29bn, WSP, AECOM, Arup — hold something like 45% of fee income, while around 30,000 sole and micro consultancies share perhaps 15% between them. The £2m–£20m regional multidiscipline firm in the middle is squeezed from both ends: too small for national frameworks, too big to undercut. Consolidation runs one way at the top (WSP absorbed Ricardo in 2025; Stantec took Hydrock) while the bottom fragments further as engineers incorporate one-person practices. A Mott MacDonald and a sole structural consultant share a SIC code and essentially nothing else.

The fee is a salary multiplier, and bidding is a "free-for-all"

Consulting engineering fees are cost build-ups: estimated hours across a scope, multiplied by graded charge-out rates — the rule of thumb is about 2.5× payroll cost over a ~1,500-hour billable year — or a percentage of construction cost calibrated to the same resource. The fee is neither remembered from past jobs nor measured off a drawing; it encodes the firm's own cost base, utilisation target and risk appetite.

There is no fee scale and no floor beneath any of it. The profession's own commentary describes bidding as a "free-for-all", with two consequences it names itself: fees driven down, and design work migrating out of consultancies into contractors and suppliers who bundle it into build agreements. The consultancy that prices its risk honestly loses to the one that does not. Add a hardening professional indemnity market — ACE speaks of members navigating a "PI Insurance storm" — and the fixed costs fall hardest on the smallest firms, who carry the same negligence exposure as the giants across a fraction of the fee base.

World-class analysis tools; a proposal built by hand

The report's technology audit finds a familiar asymmetry in an unfamiliar place. The engineering itself runs on deep, discipline-specific software — Tekla and GSA for structures, IES and Hevacomp for building services, PLAXIS for ground, Bentley across infrastructure, Revit and Navisworks for coordination. The commercial step does not. Below the giant tier with its Deltek deployments and bid teams, the fee proposal is a salary-multiplier build-up in a spreadsheet, a scope in a Word template, and a PDF — written from scratch, unpaid, by the same principal who is also the firm's entire delivery capacity.

The detail the report dwells on: ACE, the sector's trade body, publishes the standard-form appointment agreements that govern how consulting engineers are engaged — but it has never built a fee calculator. The Fees Bureau sells benchmarking data commercially; nobody gives the tool away. That absence turns out to be the pivot of the whole product-fit question.

The first "maybe" in the series

Section 10 of the report runs its established product-fit test, and for the first time in the series the answer is not a clean no. A costed fee rules out the QuoteAgent capture model — photos and a voice note cannot produce a resource build-up, and there is no shared price book to match against. But the disqualifier that closed architecture (see the companion SIC 71111 report) is absent here: no institute gives engineers a free pricing tool. What remains addressable is specific — help a small consultancy assemble and issue a fee proposal faster and more consistently, with a scope schedule aligned to ACE service schedules and a record of what was quoted and what won.

That is the gap Construct365's fee proposal builder for consultants — a product now in development — aims at, and the report is candid about why its own verdict was "maybe" rather than "yes": the micro-tier is disparate across disciplines and needs a discipline-aware scope library; the giants will never buy it, so the addressable market is a slice of the ~15% of fees held by micro-firms; and the competitor is a free spreadsheet the engineer has refined over a career. Those conditions are why the report filed the idea as a genuine future option rather than an immediate build — and they remain the tests the product has to pass.

Get the full report

The complete report covers the 71121/71122/71129 boundary and why the giants often sit outside this exact subclass, the market sizing with its stated uncertainty, the four-tier size structure, the Top 150-derived table of the ten largest firms with profiles, the discipline-level technology stack, seven documented strain points split between the giants and the tail, the five-test product-fit assessment, and a sources-and-caveats section that flags every estimate as an estimate.

Download the SIC 71122 Sector Intelligence Report (free — no email required)