In today’s fast‑moving corporate landscape, the pursuit of value through mergers and acquisitions (M&A) has become central to growth strategies for companies in the United Kingdom. But the path from negotiation room to successful deal closure is fraught with risks and uncertainties. Poorly executed deals can destroy shareholder value, derail strategic goals, and impose long‑lasting operational burdens. This is where due diligence services play a transformative role. By providing deep insights into financial, legal, operational, and strategic dimensions of a target company, these services enable dealmakers to make better decisions, mitigate risks, and improve the probability of achieving desired outcomes. This article examines whether robust due diligence can truly improve UK deal success by 30 percent, supported by the latest available data from 2025 and early 2026.
The Growing Importance of M&A Activity in the UK
UK deal activity has experienced notable fluctuations in recent years. After a rebound in total transaction value to $324.2 billion in 2024, driven by strong activity in sectors like financial services and technology, UK M&A entered a more selective phase in 2025. Deal volumes softened, with 1,478 UK transactions recorded in the first half of 2025 and total value reaching £57.3 billion, down from £65.3 billion in the same period a year earlier.
Despite these shifts, the underlying pipeline remains strong. A 2026 outlook from UK advisers shows that nearly two thirds of deal professionals expect transactional activity to increase in 2026, signaling renewed confidence that structured and well‑evaluated deals can close successfully even in uncertain markets.
However, success rates and deal outcomes vary significantly. Industry data shows that approximately 71 percent of sell‑side assignments in the UK and Ireland result in a completed deal, a relatively high rate compared to regions like DACH or Central and Eastern Europe. Yet it is critical to distinguish between deal closure and deal success, where performance post‑close aligns with strategic expectations.
What Defines Deal Success
Deal success is multi‑dimensional. It encompasses achieving strategic goals, delivering anticipated financial returns, preserving operational continuity, and capturing synergies. Historically, many mergers and acquisitions fail to meet expectations, with some global analyses indicating that 70 percent of closed deals do not reach intended objectives due to factors such as misaligned forecasts, overlooked liabilities, and cultural mismatches.
In this context, the role of due diligence services becomes crucial. When properly executed, due diligence uncovers hidden risks, clarifies valuation assumptions, and builds confidence among stakeholders. But can it deliver a tangible improvement to deal with success rates, such as a 30 percent increase? To answer this, we need to review how due diligence affects outcomes in real world scenarios.
How Due Diligence Impacts Deal Outcomes
Financial and Legal Risk Mitigation
Thorough financial due diligence helps decision makers validate historical performance, stress test future earnings projections, and identify contingent liabilities. Legal due diligence uncovers regulatory exposures, contractual obligations, and compliance shortfalls that might otherwise surface after closing, leading to value erosion or even litigation.
According to recent benchmarks, inadequate due diligence is cited as the primary reason for deal failures by more than 60 percent of executives in the UK. This highlights how often undiscovered issues derail strategic plans, despite deals technically closing.
Quantifying the financial impact of poor due diligence underscores its value. A 2026 analysis by a leading global consultancy estimated that insufficient due diligence can destroy between 15 percent and 25 percent of a deal’s value within 24 months after closing. For a mid‑sized acquisition valued at $500 million, this means potential value destruction of $75 million to $125 million due to unforeseen risks.
Operational and Strategic Integration
Due diligence also extends well beyond financial checks. Operational, commercial, IT, and environmental, social, and governance (ESG) assessments help deal teams understand how the target integrates into the buyer’s business. For example, robust analysis of technology stack compatibility can prevent post‑deal disruptions that otherwise reduce productivity and synergies.
Increasingly, due diligence procedures include cybersecurity reviews, a non‑negotiable step in the digital era. Experts now report that approximately 79 percent of executives include cybersecurity assessments in every M&A deal to prevent catastrophic breaches and regulatory penalties post‑close.
Time and Depth Tradeoffs
While due diligence drives deal quality, it also lengthens the transaction timeline. Data from Bayes Business School shows that average due diligence processing time in M&A deals has increased significantly over the past decade, from 124 days to more than 200 days.
Longer due diligence can raise costs and extend negotiation cycles, yet evidence suggests this depth correlates with better post‑deal performance. In one study, deals subjected to thorough due diligence delivered returns that were four percent higher relative to market benchmarks than deals with shorter or superficial due diligence.
Can Due Diligence Improve UK Deal Success by 30 Percent?
Based on available evidence, the answer is a qualified yes. While precise percentages vary by deal size, sector, and market conditions, the aggregated impact of high‑quality due diligence on deal outcomes is substantial.
First, due diligence sharply reduces the likelihood of unforeseen deal break costs and value destruction. If poor diligence can erode up to 25 percent of value post‑close, comprehensive diligence that avoids this erosion essentially preserves upside returns. When combined with improved decision confidence, this leads to measurable improvements in performance outcomes.
Second, improved operational and strategic alignment uncovered through diligence translates to better integration and faster synergy capture. In competitive UK sectors, companies that invest in targeted due diligence achieve clearer integration roadmaps and organisational alignment, helping actual value realization more closely match forecasted outcomes.
Finally, deeper due diligence instills investor and stakeholder confidence that can accelerate financing arrangements and reduce renegotiation risk. With UK M&A deal value reaching historically strong levels globally, enhanced scrutiny often differentiates deals that deliver long‑term results from those that simply close.
While empirical research quantifying specific percentage lifts from due diligence varies, combining insights from value protection, risk mitigation, and integration effectiveness indicates that due diligence services can indeed drive up to a 30 percent improvement in defined success metrics for many UK deals.
Key Components of Effective Due Diligence in 2026
To achieve a meaningful uplift in deal success, companies should prioritise the following areas in their due diligence frameworks:
1. Financial Forensics
Rigorous revenue and cost analysis coupled with scenario planning can expose overoptimistic forecasts and hidden liabilities early.
2. Legal and Regulatory Compliance
In jurisdictions such as the UK where regulatory scrutiny remains high, legal checks reduce risk of post‑deal penalties.
3. Technological and Cybersecurity Review
With digital risks on the rise, cybersecurity due diligence helps protect value and maintain stakeholder trust.
4. ESG and Sustainability Assessment
Environmental and social criteria are increasingly material to valuations and long‑term performance, especially among institutional investors.
5. Cultural and Human Capital Evaluation
Alignment of organisational cultures and retention of key talent frequently determines whether expected synergies materialise.
The evidence from 2025 and early 2026 suggests that due diligence services remain a critical determinant of M&A success in the UK market. While not a universal guarantee, deep and systematic due diligence addresses the core sources of deal failure, from undisclosed liabilities to integration challenges.
By reducing the risk of unforeseen value loss, smoothing operational integration, and supporting strategic clarity, effective due diligence can reasonably improve UK deal success metrics by up to 30 percent in many circumstances. As market dynamics evolve and deal complexity increases, investing in comprehensive due diligence will remain essential to achieving durable and value‑accretive outcomes. Ultimately, companies that prioritise structured diligence not only protect shareholder value but also elevate their strategic agility in an increasingly competitive deal environment.
Finance Advisory 