IN DEPTH · THE NUMBERS

The cost arithmetic.

The cost of building-while-delivering never appears on a budget line — it appears as the overrun. Here is the full comparison behind the headline: an illustrative 20-month, multi-business-unit programme of ~430 working days, priced three ways.

The City of London skyline at dusk
THE CITY OF LONDON — WHERE THE OVERRUN IS ALREADY PRICED IN · IMAGE: UNSPLASH

The alternatives, honestly stated

Versus a Big 4 support layer. £2,000–£4,000 a day at working level, £2,500–£5,500 at partner level; a five-person pyramid; and predominantly advisory — recommendations your own staff must still implement.

Versus building in-house. Seconded staff are almost never solely dedicated — BAU reclaims them exactly when the programme needs them most — and they typically haven’t run an S166 before, so tooling and governance are learned at the programme’s expense.

PROJECTED END COST — THE SAME PROGRAMME, PRICED THREE WAYS

Solid: budgeted cost. Hatched: typical overrun added by the delivery model (proj.).

≈£5.4m
BIG 4
budgeted £3.9m
£? — uncosted
IN-HOUSE
£0.8m visible
≈£1.3m
ACON
budgeted £1.2m

Big 4: budgeted £3.9m + 30–45% typical overrun. In-house: £0.8m visible — secondee time uncosted, + 35–50% overrun. ACON: budgeted £1.2m, engineered to close within 10% — call it £1.3m, all in.

Line by line

BIG 4 LAYER
IN-HOUSE BUILD
ACON
Team size
5 people, dedicated
~60% visible, plus uncosted secondee time (proj.)
A senior specialist + the pre-built system, alongside your own team
Blended day rate
~£1,850
~£600 — excluding hidden cost
~£1,350 — 27% below Big 4
Mobilisation
4–8 weeks
6–12 weeks
2–3 weeks (proj.) — tested & integrated
Typical slippage
30–45% overrun — the industry norm
30–45%+ — weak governance the leading cause
<10% target (proj.) — live float, breach alerts, freeze windows
Overrun cost exposure
+30–45% of budget (proj.)
+35–50% (proj.)
+0–10% (proj.)
Direct team cost
~£3.9m
~£0.8m visible — plus hidden cost
~£1.2m — saving ~70%
Rework share of effort
~15–25% (proj.)
~25–35% (proj.)
<5% target (proj.)

(proj.) = projection based on the published research base and the founder’s reference programme. Illustrative, from published market rates and stated assumptions — not quotations.

Why the overrun matters more than the fee

On a programme running at over £500,000 a month, a “normal” 30% overrun is roughly seven extra months — £3.5m+ of extended run-rate, plus extended skilled person engagement. ACON makes slippage visible the day it is created: overrun cost falls, reporting stays accurate, the FCA sees a controlled programme, confidence holds, attrition falls — and the working environment stays humane in what is already an extremely stressful, fast-paced undertaking.

Projected saving vs the Big 4 layer: ~£2.8m — roughly 70% — before counting avoided overrun.

Further proof points: 3–4 working days saved at mobilisation, and 7–11 working weeks saved or protected across a typical 12–24 month delivery phase, through AI-maintained linked documents (proj.). Manual reporting, reconciliation and document-maintenance effort cut by up to 80% on the reference programme.

ACON — AGILE CONTROLS · BANK-SIDE S166 DELIVERY
ACON CONSULTING IS THE TRADING NAME OF CAITLIN TAYLOR LIMITED · REGISTERED IN ENGLAND & WALES · COMPANY NO. 12681104 · REGISTERED OFFICE: 103 CEDAR WAY, GUILDFORD, GU1 1JE

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