Unpaid Invoices Are the New Mule Account: Protecting Your Business Cash from Both Ends

Every business owner in the UK has felt it: money that should be in your account is sitting somewhere else. Sometimes it's stuck in an invoice a customer hasn't paid. Sometimes it's moving through a criminal network you'll never see, using accounts that look exactly like your customers' or suppliers'.

These two problems rarely get discussed together. They should. Both are about cash leaving your control without your permission — one through delay, the other through deception. And both need systems built before the fact, not fixes bolted on after the money's gone.

The Slow Leak: Cash Trapped in Invoices

Unpaid invoices are not a paperwork issue. They're a liquidity issue. When a customer takes 60, 90, or 120 days to pay, your business is effectively lending them money — interest-free, and often without choosing to.

This is a well-known drag on SME cash flow, and it's exactly the gap that Duqu, an Amsterdam-based FinTech, has raised €1.5 million to close. The company gives businesses immediate access to money tied up in outstanding invoices, backed by an AI underwriting engine that automates 95% of the credit assessment process.

That level of automation matters. Traditional invoice finance has been slow, manual, and expensive to underwrite. If credit assessment can be largely automated, the barrier to unlocking cash quickly gets much lower — which is good news for any business tired of chasing payment terms instead of running the business.

The Fast Leak: Fraud Moving Through Legitimate Accounts

While slow payment quietly erodes cash flow, fraud moves fast — and it increasingly hides in plain sight.

The FCA's latest findings on money mules show the scale of the problem. In 2025, firms closed 238,396 suspected mule accounts — up from 184,935 in 2023. That's not a shrinking problem. It's a growing one, met with growing enforcement.

The numbers behind this are stark:

The National Crime Agency estimates over £100bn is laundered through the UK or UK corporate structures every year.
Criminals typically move funds through multiple accounts, cashing out between the second and fifth account — by which point tracing the money becomes far harder.
Account closures were highest among customers aged 26 to 39, but the sharpest year-on-year increase was among those aged 40 to 49.
Card payments were the most common cash-out method, often disguised as ordinary consumer spending through many small transactions.

The FCA's own enforcement director, Steve Smart, put it plainly: money muling "makes it harder to recover stolen cash and helps criminals move and hide the proceeds of serious offending." This isn't abstract. It's your business banking with, invoicing, or paying entities that may be part of this infrastructure without anyone realising it.

Why Both Problems Demand the Same Response

Here's the connection that matters: reactive fixes don't work for either problem.

Chasing a late invoice after 90 days is reactive. Investigating a fraudulent payment after it's cashed out through five accounts is reactive. By the time either issue reaches your desk, the damage is largely done.

What works instead is proactive infrastructure:

Automated credit and payment risk assessment — so you know which invoices are genuinely at risk before they're 60 days overdue, not after.
Faster access to cash owed to you — reducing the incentive to accept poor payment terms just to keep operations running.
Verification built into onboarding — checking who you're actually dealing with before money moves, not after.
Shared intelligence — the FCA is explicit that firms, law enforcement, and technology providers all need to work together, because criminals exploit gaps between institutions.

The FCA's review found something particularly telling: many mule accounts had been used repeatedly before being shut down, and had also been linked to earlier fraud. This points to established criminal infrastructure, not isolated bad luck. The same logic applies to persistent late payers — a pattern of delay is rarely a one-off; it's a business practice.

The Real Lesson for SMEs

Cash flow risk isn't one thing. It's two things pulling in the same direction: money you're owed but can't access, and money that could disappear through a network you never see coming.

Treating either as a problem you'll deal with "when it happens" is a mistake. The businesses managing this well are the ones building systems now — automated invoice financing to keep cash moving, and robust verification to keep bad actors out.

Neither problem is going away. The FCA data shows fraud enforcement is intensifying because the threat is too. And the fact that a fintech can now automate 95% of invoice credit checks shows the tools to fix slow payment already exist — they just need adopting.

Key takeaways

Unpaid invoices are a liquidity risk, not just an admin headache — and tools like automated invoice financing can unlock that cash immediately rather than after months of delay.
Money mule activity is rising, with 238,396 accounts closed by UK firms in 2025 alone, and criminals are using multiple accounts to make funds harder to trace.
Reactive fixes fail on both fronts — by the time a late invoice or a fraudulent payment reaches your attention, the cash is already gone or delayed.
Proactive systems protect cash from both ends: automated credit assessment for receivables, and strong verification and shared intelligence to block fraud before it moves through your accounts.
SMEs that build these systems now are protecting cash flow twice over — against slow payers and against criminal networks alike.