The Importance of Financial Controllers in Mergers and Acquisitions

When a UK business goes through a merger, acquisition or sale, most of the attention falls on the CFO, the corporate finance adviser and the lawyers. The Financial Controller rarely features in that picture — and yet, in practice, the FC often produces the core financial work that determines whether the deal runs smoothly or stalls. The quality of the data room, the defensibility of the earnings adjustments, the speed and credibility of the diligence responses: these are the things buyers actually scrutinise, and they are usually the FC’s domain. This article sets out what a Financial Controller genuinely contributes across an M&A process, and why the FC you have in place matters more to a transaction than businesses tend to assume.

Why the FC matters in a deal, not just the CFO

The division of labour in a well-run transaction is fairly consistent. The CFO leads the strategic conversations — with investors, the board, the corporate finance adviser — and owns the narrative of why the business is worth what it says it is worth. The Financial Controller produces the analytical output that has to stand behind that narrative. A buyer’s diligence team does not take the CFO’s story at face value; they interrogate the numbers underneath it, and the numbers underneath it are the FC’s work. A confident equity story supported by a data room that falls apart under questioning is worse than no story at all, because it erodes trust in everything else management has said.

That is why the FC’s contribution is often the quiet determinant of deal velocity. Transactions rarely collapse on strategy; they slow, sour or re-price on diligence — unexplained margin movements, adjustments the buyer won’t accept, a data room that arrives late and incomplete, answers that take a week when the buyer expected a day. Each of those is, at root, a financial-control problem. A capable FC keeps the process moving; a stretched or inexperienced one becomes the bottleneck that gives the buyer room to chip the price.

What the FC actually does across the deal

Preparing the data room

On a sell-side process, the FC typically owns the financial data room — the structured evidence pack a buyer’s advisers work through. Done well, that means more than dumping management accounts into a folder: it means a coherent set of monthly accounts over the relevant period, revenue analysed the way a buyer will want to see it (by customer, product, contract type), customer and supplier concentration laid out honestly, and a clear audit trail from the statutory accounts to the management numbers. The discipline is analytical, not clerical. A data room assembled as a compliance exercise — here are the documents — rarely survives a rigorous buyer; one assembled as an argument — here is the evidence for the earnings quality we’re claiming — holds up.

Quality of earnings and adjustments

Most deals turn on Adjusted EBITDA, and every adjustment to reported earnings is a small negotiation. The FC produces the quality-of-earnings analysis that supports those adjustments — identifying genuinely one-off or non-trading items, documenting each with evidence, and being ready to defend them. This is where transaction-experienced FCs earn their keep. An adjustment that looks reasonable to the seller but is poorly documented is an adjustment the buyer will strike out, and each one struck out comes off the valuation at the deal multiple. Rigorous, defensible earnings documentation is one of the highest-leverage things an FC does in a sale.

Leading the diligence response

Once a buyer is engaged, the FC usually runs the financial side of diligence response: managing the flow of questions, coordinating with the auditors, and turning buyer queries around quickly and accurately without needing the CFO to intervene on every point. Speed and reliability here shape the buyer’s confidence directly. A process where questions are answered crisply and consistently reads as a well-run business; one where answers are slow, contradictory or defensive reads as a business with something to hide — and invites deeper, more sceptical digging.

Holding the day job together at the same time

The most underestimated demand of a live transaction is that the ordinary finance function has to keep running while the deal work happens. Monthly close still has to complete, the board still needs its reporting, and — crucially — the business needs to keep hitting its numbers, because a dip in trading during diligence is exactly the kind of thing that re-prices a deal. Transaction work absorbs a large share of finance-team capacity, and the FC who can maintain business-as-usual discipline through the process, rather than letting it slip while everyone focuses on the deal, protects the valuation as much as any single adjustment does. This is why deal-active businesses often need to expand finance capacity ahead of a process rather than assume the existing team can absorb it.

Post-deal integration

The FC’s role doesn’t end at completion. On the buy-side, integrating the acquired business’s finances — aligning accounting policies, consolidating reporting, harmonising controls, often migrating systems — falls largely to financial control. Integration done well is what turns the deal thesis into realised value; integration done badly is where synergies quietly evaporate. For acquisitive businesses running serial bolt-ons, a strong FC with integration experience is not a nice-to-have but a core part of the platform’s ability to keep buying and absorbing.

The FC profile that suits a deal-active business

Not every excellent Financial Controller is the right FC for a business heading into a transaction, and the difference is specific. The strongest technical FCs from an audit or statutory-reporting background are not automatically strong in a deal, because diligence response rewards a different instinct — treating the data room as an analytical argument to be defended rather than a compliance pack to be filed. The FCs who tend to excel in M&A-active roles have genuine transaction exposure: either prior advisory experience on buy-side or sell-side diligence, or industry experience at a business that has been through a funding round, an acquisition or an exit. That exposure teaches the analytical intensity and the buyer’s-eye view that diligence demands, and it is more predictive of success in a deal context than technical credentials alone.

For a business anticipating a transaction — a planned sale, a fundraising, or a buy-and-build strategy — this is worth thinking about before the process starts, not during it. The point to strengthen the finance function is ahead of diligence, when there is time to get the data room, the earnings analysis and the team capacity right. Discovering mid-process that the FC function can’t carry the transaction load is an expensive time to find out.

Where finance-control problems re-price deals

It is worth being concrete about how weak financial control actually costs a seller money, because the failures are consistent and largely avoidable. The most common is a data room that arrives incomplete or disorganised, forcing the buyer to ask for basics that should have been ready — which slows the process and signals a business that isn’t on top of its numbers. A close second is earnings adjustments that can’t be defended: an Adjusted EBITDA built on add-backs the seller believes in but hasn’t evidenced, which the buyer strips out one by one, each reduction multiplied by the deal multiple. Then there are the surprises — a working-capital pattern nobody flagged, a customer concentration the seller downplayed, a reconciliation between statutory and management accounts that doesn’t hold — each of which hands the buyer a reason to renegotiate. None of these is a strategic failure; all of them are financial-control failures, and all of them are the kind of thing a transaction-experienced FC anticipates and closes off before the buyer ever sees them. That is the real argument for taking the FC seriously as a deal role rather than a back-office one.

Related financial controller insights

Adrian Lawrence

Adrian Lawrence FCA is the founder of FD Capital and a Fellow of the Institute of Chartered Accountants in England and Wales (ICAEW). He holds a BSc from Queen Mary College, University of London, and has over 25 years of experience as a Chartered Accountant and finance leader working with private, PE-backed and owner-managed businesses across the UK. He founded FD Capital to connect growing businesses with the Finance Directors and CFOs they need to scale — and personally interviews candidates for senior finance appointments.