Why Mutuality of Obligations Is IR35’s Greatest Trap
Ignore MOO and You Risk Everything
Every UK contractor knows about IR35. But Mutuality of Obligations (MOO)? That’s the unseen tripwire. The one that, if missed, can destroy your case. In 2025/26, the issue is only intensifying.
What Is MOO, Really?
MOO tests whether the client must offer work and you must accept it. If so, you look like an employee. If not, you’re independent. Sounds simple. It isn’t.
HMRC’s view is aggressive:
HMRC claims MOO exists in nearly every engagement.
Their guidance is vague and self-serving.
Judges disagree, but HMRC persists.
Why Is MOO So Damn Difficult?
It’s invisible: Unlike control or substitution, MOO is about expectations. There’s rarely paperwork.
It’s misunderstood: Clients and agencies often don’t get it. Their contracts are full of contradictions.
HMRC Weaponises It: They use MOO to tip borderline cases into ‘inside’ IR35, regardless of the working reality.
“The courts have repeatedly slammed HMRC’s MOO approach. But contractors still lose cases.”
Contractor Mistakes: How You’re Getting Burned
Relying on generic contracts
Failing to document gaps between assignments
Accepting rolling work without clear scope
Letting clients dictate your hours or workload
The 2025/26 Headache
With more HMRC scrutiny and automated status tools, MOO is being tested by algorithms, not humans. These tools ignore nuance.
It’s easy to get flagged as inside IR35 even when you shouldn’t be.
How Contractors Can Fight Back
Here’s how to take control:
Demand a project-based contract. Every assignment should have a clear deliverable and end date.
Refuse blanket clauses. Don’t let clients add terms requiring you to accept more work.
Document the gaps. Keep records of downtime between contracts.
Push back on client control. If they assign tasks on a whim, insist on sticking to the scope.
| Pitfall | How to Counter |
|---|---|
| Rolling work offers | Insist on new contracts for new work |
| No evidence of gaps | Record dates and tasks for every engagement |
| Client expects you on call | Clarify in writing: you’re not obliged to accept extra work |
| Standardised agency contracts | Negotiate; get legal review |
The Time to Act Is Now
Too many contractors are sleepwalking into IR35 traps because of MOO. It’s not just a legal technicality. It’s the difference between freedom and being shackled as a disguised employee.
Next Steps for Contractors
Review your contracts immediately.
Educate your clients and agencies.
Invest in professional status reviews.
Don’t wait for HMRC to come to you—prove your independence now.
Stop treating MOO as an afterthought. Make it your priority.
