Case Study
Region-specific basket optimisation: the UK gilt crisis
How systematic optimisation discovered UK gilt vulnerability using historical data — and why a global basket would have failed.
The problem
In September 2022, UK gilt prices collapsed approximately 42% after the Truss/Kwarteng mini-budget triggered a liability-driven investment (LDI) unwind across UK pension funds. The fiscal shock — an unfunded tax cut announced without OBR oversight — overlaid a global rate-hiking cycle that was already pressuring fixed income globally.
A standard 60/40 portfolio holding UK gilts at 40% weight lost approximately 21% over the January–October 2022 period. UK equities fell -13.7% while UK gilts fell -30.4%. The diversification benefit of the 60/40 allocation inverted entirely.
What RegimeR found
The systematic weight optimiser was tasked with finding regime-conditional basket weights that maximise risk-adjusted returns for the UK market across all four regimes. The quantitative optimisation process was given no information about the gilt crisis specifically — it operated on monthly return data for UK-relevant instruments across the full backtest window.
The optimiser independently set UK gilts weight to 0% across all four regimes — Contraction, Stagflation, Transition, and Expansion — replacing gilt exposure with short-duration cash equivalents and gold.
Permutation validated: statistically significant (p < 0.001, z = +3.54) across 30,000 permutation simulations.
The 2022 outcome
During the January–October 2022 period encompassing the gilt crisis:
| Portfolio | Return | vs Benchmark |
|---|---|---|
| 60/40 benchmark (UK equities + UK gilts) | -21.0% | — |
| Standard Transition basket (with gilts) | -21.8% | -0.8pp |
| Rate-shock adjusted basket | -12.5% | +8.4pp |
| RegimeR GB optimised basket (gilts = 0%) | -5.3% | +13.1pp |
The standard Transition basket — the one a global implementation would have used — underperformed the 60/40 benchmark by 0.8 percentage points. Holding gilts in the defensive allocation actively destroyed value during a UK-specific gilt crisis.
Why it matters
This finding is not a retrospective patch applied after the gilt crisis. It is a structural insight about UK fixed income market microstructure that the optimiser discovered from the return correlation structure.
UK gilts lack the safe-haven premium that US Treasuries possess. In US stress episodes, Treasuries typically rally as capital flows to safety. UK gilts do not reliably exhibit this behaviour because:
LDI leverage
UK pension funds hold gilts on leveraged mandates. In stress, margin calls force gilt liquidation — selling pressure at the moment the safe-haven bid should appear.
Pro-cyclical institutional flows
UK institutional investors are concentrated holders of gilts. Their regulatory and liquidity constraints create correlated forced selling during stress events.
Smaller market, less global demand
The gilt market is smaller than the US Treasury market. During global stress, international capital flows to Treasuries, not gilts.
Fiscal credibility sensitivity
UK gilt prices are more sensitive to fiscal policy announcements than US Treasuries, creating an additional source of correlation with domestic equity risk.
The optimiser captured these dynamics without being told about them. By observing that gilt returns during Contraction and Stagflation regimes were insufficiently negative-correlated with equity drawdowns, it concluded that gold and short-duration cash were superior defensive assets for a UK portfolio.
The commercial implication
A UK institutional investor running RegimeR with the standard global basket — which allocates 20–40% to gilts across stress regimes — would have been worse off than a passive 60/40 holder during the 2022 gilt crisis.
Region-specific baskets are not optional. A global one-size-fits-all allocation that works for US investors can actively harm UK investors during UK-specific stress events.
The structural features that make gilts poor crisis hedges — LDI leverage, concentrated institutional ownership, smaller market size — are long-term characteristics of the UK fixed income market.