The Bank of England's SONIA Stakeholder Advisory Group (SSAG) convened on 25 September 2026 to assess the operational and definitional consequences of the Bank's ambition to move Real Time Gross Settlement (RTGS) and CHAPS towards near 24-hour, seven-day-a-week operation. The discussion centred on preserving the integrity of the Sterling Overnight Index Average (SONIA), the primary benchmark for sterling money markets, which currently publishes at 09:00 based on data submitted by 07:00.
Key Takeaways
- BoE SSAG reviewed impact of near 24/7 CHAPS settlement on SONIA benchmark methodology and operations.
- Unsecured overnight market stable: £55bn daily volumes, 1.9bp spread to Bank Rate; MMF inflows £15bn YTD.
- Strong industry preference to retain 09:00 SONIA publication; later fix risks disrupting product processing.
- Weekend CHAPS opening raises questions on weekend SONIA publication vs. weekday incorporation.
- BoE and HM Treasury reviewing statutory data collection powers to safeguard SONIA coverage amid market evolution.
Executive Intelligence Brief
Retrospective Market Stability Confirmed
The Group noted the unsecured overnight market remained stable through the review period, with daily volumes averaging around £55 billion and the spread to Bank Rate fluctuating close to 1.9 basis points. Money-market funds recorded collective inflows of approximately £15 billion since the start of the year, increasing allocation to the overnight tenor following updated liquidity guidance and heightened geopolitical tensions. Repo-market volatility and month-end spikes were lower than the previous year, indicating resilient short-dated funding conditions.
Extended Settlement Hours Challenge SONIA Conventions
The Bank consulted over summer 2026 on extending settlement hours and intends to return to industry in Q1 2027 with feedback themes. Under one scenario analysed, CHAPS could close at 18:00 with the next session opening at 20:00, creating a two-hour window where the CHAPS value date diverges from the calendar date. This raises the prospect of market participants adopting timestamp-based conventions for trade booking, potentially accelerating or delaying decisions to manage interest calculations.
Participants highlighted that many Sterling Money Market Data (SMMD) reports are automated, but the ability to resubmit or regenerate prior-day data would be critical under extended hours. The Group indicated a strong preference to preserve the current 09:00 SONIA publication time, noting a later fix could disrupt processing and fulfilment of SONIA-referenced products.
Weekend Settlement Introduces Structural Questions
The proposed Sunday and potential full-weekend CHAPS opening prompted debate on whether weekend activity would differ structurally from weekday volumes and rates. The Group discussed whether SONIA should be published for weekends or if weekend transactions should be incorporated into the following weekday's calculation, a decision with direct implications for the benchmark's representativeness and the accrual mechanics of linked contracts.
Data Collection Powers Under Review
Separately, the Bank and HM Treasury are reviewing the statutory powers used to collect sterling money market information. The review aims to ensure sufficient coverage and visibility of market activity as structures, regulation, infrastructure, and booking locations evolve. The Bank may seek powers to collect data on material sterling money market activity in group entities to preserve SONIA coverage if necessary.
Forward Outlook and Key Milestones
The Bank's analysis of extended hours scenarios continues. The next confirmed milestone is Q1 2027, when the Bank will publish themes from the RTGS/CHAPS consultation and outline next steps. Concurrently, the outcome of the joint BoE/HM Treasury review of data gathering powers will determine the future regulatory framework for SONIA's input data. The ONS consultation on economic data release times, moved to 07:00 during Covid, was also noted as a relevant market structure development.
