Introduction
Corporate Interest Restriction (“CIR”) is one of the UK’s most significant anti-avoidance measures affecting large groups and companies with substantial financing costs. Introduced from 1 April 2017, the rules are designed to limit the amount of tax relief groups can obtain for net interest and other financing expenses.
The regime implements the OECD’s Base Erosion and Profit Shifting (“BEPS”) Action 4 recommendations and is intended to prevent multinational groups from reducing taxable profits through excessive debt funding.
Although originally targeted at large multinational groups, the CIR rules can apply equally to domestic groups and private businesses where financing costs exceed the relevant thresholds.
This article provides an overview of the UK CIR regime, including how the rules operate, key exemptions, and practical considerations for businesses.
Overview of the CIR Regime
The CIR rules broadly restrict a group’s deductions for:
- Loan interest;
- Amounts economically equivalent to interest;
- Financing expenses arising under derivatives or alternative finance arrangements; and
- Certain foreign exchange movements and guarantee fees.
The restriction applies at the level of the worldwide group rather than individual entities.
Where applicable, the rules limit deductions for a group’s net tax-interest expense to the lower of:
- The group’s “fixed ratio” amount (generally 30% of UK tax-EBITDA); or
- The group’s “group ratio” amount, if elected into.
The legislation is primarily contained within Part 10 of the Taxation (International and Other Provisions) Act 2010 (“TIOPA 2010”).
When Do the Rules Apply?
The CIR rules apply where:
- A worldwide group has UK tax-interest expense; and
- The group’s aggregate net tax-interest expense exceeds the £2 million de minimis threshold in a 12 month accounting period.
The £2 million allowance applies per worldwide group and is allocated across UK companies within the group.
Groups with net tax-interest below this threshold are generally outside the regime and no restriction arises.
Key Concepts
Net Tax-Interest Expense
Net tax-interest expense broadly represents the group’s tax-deductible financing costs less taxable financing income.
It is calculated using tax principles rather than accounting treatment.
Examples include:
- Bank loan interest;
- Intercompany financing costs;
- Discounting arrangements;
- Certain lease financing elements; and
Derivative financing costs.
Tax-EBITDA
Tax-EBITDA is broadly the group’s taxable profits before:
- Interest;
- Tax;
- Capital allowances; and
- Amortisation/depreciation adjustments.
The fixed ratio rule allows deductions of up to 30% of tax-EBITDA.
For example:
| Item | Amount |
| Tax-EBITDA | £20 million |
| 30% fixed ratio | £6 million |
| Net tax-interest expense | £8 million |
In this example, £2 million of interest would potentially be restricted unless relief is available under the group ratio rule.
The Fixed Ratio Rule
The fixed ratio rule is the default method.
Under this approach, a group’s interest deductions are capped at:
This aligns with the OECD’s recommended benchmark for acceptable leverage. Any excess interest above the permitted amount is disallowed for the period, although it may potentially be carried forward.
The Group Ratio Rule
The group ratio rule recognises that some groups are commercially highly leveraged.
Where elected, the allowable deduction may exceed 30% of UK tax-EBITDA if the worldwide group’s external gearing supports a higher ratio.
The calculation compares:
- The worldwide group’s qualifying net third-party interest expense; to
- Its accounting EBITDA.
This can provide significant additional capacity for infrastructure groups, real estate businesses, and private equity-backed structures.
However, the group ratio is capped at 100% of UK tax-EBITDA.
Interest Allowance and Restriction
If a group’s net interest expense exceeds its available interest capacity, the excess becomes a “restricted amount”.
The restriction is allocated amongst UK group companies via a:
- A CIR return; or
- HMRC allocation rules where no return is filed.
The appointed reporting company is responsible for filing the return on behalf of the group.
Public Infrastructure Exemption
A Public Infrastructure Exemption (“PIE”) may apply to qualifying infrastructure companies involved in:
- Public benefit infrastructure assets;
- Long-term infrastructure projects; and
- Certain regulated activities.
Where conditions are met, qualifying interest expense can be excluded from the CIR calculation.
This exemption is particularly relevant to sectors such as:
- Energy;
- Utilities;
- Transport; and
- Social infrastructure.
Carry Forward Provisions
The CIR regime includes carry forward mechanisms for:
Restricted Interest
Disallowed interest can generally be carried forward indefinitely and potentially deducted in future periods where sufficient interest capacity exists.
Unused Interest Allowance
Where a group has excess interest capacity, this may also be carried forward for up to five years.
This can provide valuable flexibility for groups with fluctuating profitability or financing arrangements.
Administrative Requirements
Groups within CIR may need to:
- Appoint a reporting company;
- Prepare annual CIR computations;
- File a CIR return within 12 months of the period end; and
- Maintain supporting documentation.
Even where no restriction arises, filing a return may still be beneficial to preserve unused interest allowance capacity.
Practical Issues and Common Challenges
Complexity
The CIR rules are highly complex and frequently require detailed analysis of:
- Group structures;
- Financing arrangements;
- Tax and accounting adjustments; and
- Elections and exemptions.
Interaction with Other Rules
CIR interacts with numerous other tax provisions, including:
- Transfer pricing;
- Hybrid mismatch rules;
- Anti-hybrid financing provisions;
- Loss restrictions; and
- Withholding tax obligations.
Care is required to avoid unexpected outcomes.
Impact on Transactions
The rules can significantly affect:
- Acquisitions;
- Group restructurings;
- Refinancing arrangements; and
- Real estate or infrastructure investments.
Modelling CIR implications early in a transaction process is therefore essential.
Conclusion
Corporate Interest Restriction remains a key area of UK corporation tax compliance for large and highly leveraged groups. While the £2 million de minimis threshold excludes many smaller businesses, groups with significant financing costs must carefully assess their exposure.
Given the technical complexity of the regime and its interaction with wider international tax rules, proactive planning and robust compliance processes are essential. Businesses should regularly review financing structures, monitor interest capacity, and consider whether elections such as the group ratio rule or Public Infrastructure Exemption may improve their position.
As HMRC continues to scrutinise financing arrangements, CIR is likely to remain an important focus area for corporate tax governance and risk management.
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