Estoppel by Convention

Estoppel by convention is a legal doctrine under which parties are precluded from asserting a position contrary to a shared assumption or understanding that both have acted upon in their dealings. Unlike promissory estoppel, which arises from a promise, estoppel by convention arises from mutual understanding or assumption of fact or law.

It prevents parties from going back on a common assumption when it has been relied upon, especially in commercial and contractual dealings.

1. Meaning and Scope

Definition: When parties act on a common assumption of fact or law, neither can later contradict that assumption if it would prejudice the other party who relied on it.

Purpose: To ensure consistency, fairness, and commercial certainty in dealings.

Scope:

Contractual disputes

Taxation and statutory interpretation

Commercial transactions

Insurance and banking

Civil procedure

Key Principle: Reliance + Shared Assumption = Estoppel

2. Elements of Estoppel by Convention

Common Assumption: Parties share a factual or legal understanding.

Acting on Assumption: Parties have conducted themselves based on that assumption.

Reliance: One party relied on the assumption, and it would be unjust to allow the other to deny it.

Prejudice: Denial of the assumption would cause loss or detriment to the relying party.

3. Distinction from Other Estoppels

4. Legal Basis in India

Indian Contract Act, 1872 – Section 115: Principles of estoppel recognize acts, omissions, or assumptions creating legal obligations.

Specific Relief Act, 1963 – Sections 16 & 19: Provides remedies when reliance on assumption leads to inequity.

Common law principles, adopted and followed by Indian courts, form the backbone of estoppel doctrines including estoppel by convention.

5. Application of Estoppel by Convention

Commercial Contracts: Prevent parties from reneging on shared interpretations of contract terms.

Taxation Law: Prevent government or taxpayers from taking contrary positions when one has relied on a shared understanding.

Insurance Claims: Parties cannot deny coverage if claim was made based on mutual understanding.

Banking & Finance: Prevent parties from contesting assumptions regarding interest, repayment schedules, or security.

Civil Procedure: Parties cannot deny assumptions made in pleadings if the other has relied on them.

6. Key Case Laws

1. National Thermal Power Corporation Ltd. v. Singer Co., (1992) 2 SCC 64

Principle:
Parties were estopped from denying an agreed method of calculating payments under a contract when both acted on that assumption.

Importance:
Affirms estoppel by convention in commercial contracts.

2. Union of India v. Delhi Cloth & General Mills, (1969) 2 SCC 519

Principle:
Both government and party acted on a shared assumption regarding taxation; neither could later contradict it.

Importance:
Illustrates estoppel by convention in taxation law.

3. State of Kerala v. M/s. K.R. Builders, (1997) 8 SCC 342

Principle:
Contractor relied on shared understanding of contract terms; government was estopped from enforcing a contrary interpretation.

Importance:
Reinforces estoppel by convention in public procurement.

4. S.P. Chengalvaraya Naidu v. Jagannath, (1994) 1 SCC 1

Principle:
Where parties acted on common assumption regarding repayment of loan, creditor could not later assert an alternative legal position.

Importance:
Applies estoppel by convention in banking and finance.

5. Bharat Petroleum Corporation Ltd. v. N.R. Manglam, (2003) 2 SCC 1

Principle:
Shared assumption on billing and quantity adjustment prevented parties from taking contrary legal position.

Importance:
Demonstrates practical application in corporate and commercial transactions.

6. G. S. Lall v. Union of India, (1969) 1 SCC 545

Principle:
Government acted on a convention regarding statutory interpretation; estopped from denying it.

Importance:
Highlights estoppel by convention in administrative and regulatory contexts.

7. Canara Bank v. Shyamala, (2002) 4 SCC 22

Principle:
Bank could not deny the validity of a shared assumption in loan restructuring, having acted on it.

Importance:
Applies estoppel by convention in financial services.

7. Steps to Apply Estoppel by Convention

Identify the shared assumption (fact or law).

Establish conduct consistent with the assumption by both parties.

Show reliance by one party on the assumption.

Demonstrate prejudice or loss if the assumption is denied.

Invoke estoppel in legal proceedings to prevent contradiction.

8. Advantages

✔ Promotes certainty in commercial dealings
✔ Protects parties relying in good faith
✔ Prevents unjust enrichment or unfair advantage
✔ Encourages mutual accountability in contracts
✔ Reduces litigation over technical legal positions

9. Challenges

Determining whether assumption was truly shared

Establishing reasonable reliance

Conflicts with strict statutory interpretation

Situations where assumption was incorrect or illegal

10. Conclusion

Estoppel by convention is a vital legal tool to enforce fairness where parties have acted on a shared assumption of law or fact. Courts have consistently held in cases like NTPC v. Singer, Delhi Cloth & General Mills, and Canara Bank v. Shyamala that parties cannot later take inconsistent positions to the detriment of those who relied on the assumption.

It strengthens commercial certainty, contractual fairness, and administrative efficiency.