Hold sustainability data to the standard you already apply
Assurance turned sustainability disclosure into a controls problem, which puts it squarely in your territory. Horizon ESG gives non-financial data the lineage, approval workflow and reproducibility you would demand of anything reaching a published report.
Every published figure traces back to a document
Your assurance provider will not ask whether the total adds up. They will ask where each half of it came from, which version of which factor was applied, and who approved the change.
Immutable change log
14 source documents
DEFRA 2026, v1.2
What it saves you. Fieldwork spent reconstructing evidence is the single largest driver of assurance cost. This is that evidence, already built.Calculation Methodology
Why this landed on your desk
ESG moved from fourteenth to ninth in tracked CFO priorities in a single year, the largest upward shift of any category. That is not a change in enthusiasm. It is what happens when a disclosure becomes subject to assurance.
Assurance is live
Limited assurance applies to the largest reporters now, and ISSA 5000 covers engagements for periods beginning on or after 15 December 2026.
Providers test controls
Your assurance provider examines process, documentation and traceability, not just whether the totals add up.
The data was never controlled
Most sustainability numbers were assembled in spreadsheets by people who were never asked to evidence them to audit standard.
The exposure is yours
A figure in a published report that cannot be substantiated is a governance problem long before it is a sustainability one.
The gap is evidence, not arithmetic
Sustainability teams are generally good at the subject matter. What they were never resourced to build is a control environment. Emission factors get chosen without recording which version was used. Figures get revised without a log of who revised them or why. Estimates get made without being labelled as estimates. None of that is negligence, it is what happens when reporting grows out of a spreadsheet rather than out of a system.
It becomes your problem at the point of assurance, because the cost and difficulty of an engagement is driven less by the complexity of the numbers than by how much of the fieldwork is spent reconstructing evidence that should already exist.
What assurance providers find
- Figures assembled in spreadsheets, offline
- Emission factor sources undocumented
- No record of who changed a value, or why
- Estimates presented as measurements
- Prior year cannot be reproduced after a factor update
- Preparer and approver are the same person
What they should find
- Every figure traceable to a source document
- Factor source and version stored on the number
- Immutable change log with user and timestamp
- Estimates labelled, with the basis shown
- Prior periods reproducible on the original method
- Segregation of duties enforced by the system
What Horizon ESG gives the finance function
- Datapoint-level lineage. Every disclosed figure links to the document it came from. Your assurance provider traces it in clicks rather than requesting a file and waiting two days.
- Enforced segregation of duties. Role-based permissions separate data entry, review and approval, rather than relying on people remembering the convention.
- An immutable audit trail. Who changed what, when, from what value to what value. It cannot be edited after the fact, which is what makes it a control rather than a note.
- Reproducibility. Regenerate a prior period on the methodology and emission factors that applied at the time, after both have since been updated. Most platforms cannot, and it becomes visible at the second assurance cycle.
- Labelled estimates. Where a figure is estimated rather than measured, the report says so and shows the basis. Silent estimation is the finding nobody wants.
- Intelligence that shows its working. Nova accelerates collection and factor matching, and every output it produces is sourced, labelled and recorded in the same audit trail as manual entry, subject to human approval before it reaches a report.
- Published pricing. Rates are on the website, so you can size the decision before committing to a procurement cycle.
What is coming that affects the budget
Three items in the next eighteen months carry a cost implication worth planning for now.
- ISSA 5000 applies to engagements covering periods beginning on or after 15 December 2026. Expect your provider to scope more fieldwork on controls than on recalculation.
- UK SRS S1 and S2 arrive for listed companies from financial years beginning 1 January 2027, on a comply-or-explain basis confirmed in the FCA’s final rules on 30 September 2026. Every gap you explain becomes a published statement; see how to write a defensible explanation. It is ISSB-based, not ESRS-based. See our guide to who reports and when.
- SBTi Corporate Net-Zero Standard V2 takes effect on 31 January 2027 and introduces mandatory assurance and climate transition plans for larger companies. This one catches organisations through a voluntary target commitment rather than a regulation, which is why it is frequently missed in planning.
Where this sits alongside the sustainability team
This is a division of labour rather than a transfer. The sustainability team holds the subject matter judgement, materiality and framework interpretation. Finance holds the control environment and the relationship with the assurance provider. The platform is what lets both work on the same data without one side rekeying the other’s output.
Want the operational view? See the same platform from the sustainability team’s perspective, covering customer data requests and the reporting cycle.
Frequently Asked Questions
Why is sustainability reporting becoming a finance responsibility?
Because assurance made it one. Limited assurance turns sustainability disclosure into a controls and evidence problem, which is the discipline finance already owns. Sustainability teams hold the subject matter expertise; finance holds the control environment. In practice the reporting increasingly sits with finance while the sustainability team remains the technical author. ESG moved from fourteenth to ninth in tracked CFO priorities in a single year, the largest upward shift of any category.
What is ISSA 5000 and when does it apply?
ISSA 5000 is the international standard for sustainability assurance engagements. It applies to engagements covering periods beginning on or after 15 December 2026, so for most calendar-year reporters it lands in the next cycle rather than a distant one. It formalises what assurance providers examine: process, documentation, traceability and controls, rather than a recalculation of your totals.
How much does sustainability assurance cost?
Assurance fees vary by scope, provider and the state of your evidence, and no honest vendor will quote you a figure for your auditor’s time. What you can control is the second variable. The largest driver of assurance cost is how much of the engagement is spent reconstructing evidence that should already exist. Companies that can trace a published figure to its source document in the system spend markedly less of the engagement on back-and-forth than companies producing evidence on request.
What controls should sustainability data have?
The same ones you would expect over any figure that reaches a published report: enforced segregation between whoever enters data and whoever approves it, an immutable log of who changed what and when, documented methodology including emission factor sources and versions, and the ability to reproduce a prior period on the methodology that applied at the time. If a change log can be edited, it is not a control.
Does CSRD still apply to us?
Only above 1,000 employees and 450 million euro turnover, both together, following the Omnibus I Directive that came into force on 18 March 2026. Scope fell from roughly 50,000 companies to roughly 5,000 across the EU. Being out of direct scope does not remove the reporting burden: customer and lender data requests continue, UK SRS arrives for listed companies from FY2027, and SBTi’s Corporate Net-Zero Standard V2 introduces mandatory assurance for larger companies from 31 January 2027, which catches many companies through a voluntary commitment rather than a regulation.
What does Horizon ESG cost?
Pricing is published rather than quoted: 20 pounds per user per month on Pro for up to five users, 15 pounds per user per month on Business for five to fifty, and bespoke Enterprise pricing. No setup fees, and a two-month free trial with full platform access. Most vendors in this category do not publish rates at all, which makes budgeting a sales process. See pricing for the detail.
The most useful demo we run for finance teams starts with last year’s management letter or assurance findings. We will show you which of them the platform closes and which it does not.
Put it under control before the engagement starts
See the lineage, the change log and the approval workflow on real data, in fifteen minutes.
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