Aggregation is one of the least-understood mechanics in solicitors' professional indemnity insurance, and one of the most consequential in conveyancing. Whether a set of related files collapses into a single claim under the SRA Minimum Terms and Conditions (MTC), or stays as separate claims each drawing on its own limit and retention, can change the financial outcome for a firm and its clients by several million pounds. This entry sets out the rule, the leading authorities, and how it plays out on conveyancing files in practice.
The SRA Indemnity Insurance Rules 2020, Schedule 1 clause 2.5 (which mirrors the long-standing MTC wording) provides that the insurance may treat as one claim all claims arising from:
Where aggregation applies, one each-and-every limit (a minimum of £2 million for most firms, £3 million for incorporated practices) responds to the aggregated claim, and one self-insured excess is deducted. Where it does not apply, each claim draws on the limit separately.
The Supreme Court in AIG v Woodman gave the definitive modern analysis. Lord Toulson broke the clause into four limbs and held, on the fourth ("similar acts or omissions in a series of related matters or transactions"), that the test requires an intrinsic relationship between the matters or transactions themselves, not merely a common cause. Transactions are related where they share a real connection in the sense that they are part of a single project, common venture, or interdependent scheme. The court emphasised that aggregation is a factual, evaluative exercise. A shared solicitor, a shared error, or a shared category of client is not enough on its own.
Earlier, in Countrywide Assured, the Commercial Court considered conveyancing files infected by developer fraud. Morison J held that the transactions were sufficiently related to aggregate because they arose from a common fraudulent scheme, and each purchase was part of the same overarching venture. The decision has been treated as consistent with the later reasoning in Woodman: the unifying feature was the scheme itself, not merely that the same solicitor had signed off each file.
In Standard Life v Oak Dedicated, the court confirmed that aggregation clauses are to be read on their terms — the specific words the parties agreed to use — rather than by importing tests from other insurance contexts. For SRA MTC purposes, the four-limb structure of clause 2.5, as parsed in Woodman, is the starting point.
Three fact patterns come up regularly. A firm acts for buyers on a single new-build development where the developer has committed title fraud — the shared scheme typically aggregates under limb four. A firm acts for a lender on a buy-to-let mortgage book and gives negligent title advice on adjacent plots in the same title register — aggregation is likely where the plots are part of one estate. A firm gives the same defective advice on unrelated retail purchases across the country — aggregation is unlikely because the transactions have no intrinsic connection beyond the shared error.
Illustrative example only. A solicitor firm acts for 30 buy-to-let buyers on a single new-build development. Later, the developer's fraudulent title arrangements are discovered, affecting all 30 transactions. Total loss across the buyers is £6 million.
If the claims aggregate as a "series of related matters" under Woodman limb four — because the buyers were all part of the same development scheme — the insurer treats them as one claim of £6 million, subject to a single £2 million each-and-every limit. Recovery is then capped at £2 million, with a £4 million shortfall potentially falling back on the firm and the buyers.
If the claims do not aggregate — 30 separate transactions — each buyer's claim is covered up to the £2 million limit, with 30 separate excesses. Total insurer exposure could reach a much higher figure, subject to the aggregate limit for the policy year. Aggregation therefore usually favours the insurer on high-value multi-transaction losses. It can, though, simplify defence and notification.
Aggregation risk is a live consideration when choosing PI limits. A firm with a conveyancing book concentrated on new-build schemes, buy-to-let developments, or lender panel work should consider the aggregate exposure on any one scheme going wrong, not just the value of an average file. Excess-of-loss cover above the MTC minimum can be arranged where the exposure justifies it, and Apex Insurance Brokers can walk through how the limbs of clause 2.5 apply to a specific book of work.
For the wider framework, see the solicitors PI insurance guide. Related professional PI regimes are covered in the architects, accountants and surveyors guides.
Apex Insurance Brokers Limited is authorised and regulated by the Financial Conduct Authority. Firm reference number 724952. This entry is general information, not advice on any particular policy.