T+1 Is an operations programme, until it becomes a CASS problem

What does T+1 settlement mean for CASS? We look at lessons from the US and where accelerated settlement could touch client money, custody assets, reconciliations and settlement controls.

On 11 October 2027 the UK moves to T+1. The FCA's most recent update is specific about the pace of change it expects from firms. These firms should already be well advanced with implementation and internal testing/readiness activity ahead of the formal market-wide testing scheduled from 2027. Most of the effort to implement T+1 is likely to sit with Operations and Technology: matching, funding, settlement, and exception handling. For firms subject to CASS, the more specific question is whether the controls protecting client money and custody assets remain robust once there is less time to catch things going wrong.

Four key considerations

• CASS 6 and CASS 7 are not changing. What changes is the operating environment those rules sit in.
• The US transition, in May 2024, went smoothly, but only after roughly three years of coordinated preparation that most UK firms have not had.
• The main risk is not settlement failure itself. It is losing the time to identify a failure before it becomes a client money or custody issue.
• Testing needs to go beyond the most common, expected scenarios and include real historical settlement failure reasons.

Same rules, tighter margin

T+1 does not rewrite CASS 6 or CASS 7. Firms will still safeguard custody assets, segregate client money, keep adequate records and run the required reconciliations. What changes is the speed at which everything upstream of the specific CASS controls is needed including allocation, confirmation, matching and settlement. The CASS controls may look identical on paper, while the processes feeding them and the risks underpinning them have changed.

What the US experience does and doesn't tell us

When US markets moved to T+1 in May 2024, the feared spike in settlement failures largely didn't materialise and industry reporting since has put fail rates broadly in line with T+2. That's a reasonable basis for confidence, but it followed several years of coordinated work between SIFMA, ICI and DTCC, plus heavy investment from firms in automation. The FCA has been explicit that UK firms shouldn't assume the same result. Unlike the US's single-CSD model, UK and European settlement runs across multiple CSDs, involves materially more cross-border and multi-currency positions, and carries fund-distribution complexity the US market didn't have to contend with in the same way, which is why a direct read-across from the US result is unlikely to hold in full.

It also means firms aren’t all starting from the same place. Those with an existing US business can draw directly on their own US operations teams’ experience, the funding and control adaptions they made for May 2024 are a live reference point for their UK build, not a hypothetical one. Firms without a US business don’t have that shortcut internally and should treat it as a known gap to close deliberately, through industry testing programmes, external advisers, or others who lived through the US transition, rather than assume it closes itself by 2027.

The open question for UK go-live is whether fail rates settle back to something close to today’s levels once the dust clears, or drift higher for a period. If they drift higher, the follow-on question is whether that shows up as a manageable bedding-in effect, or as a sustained rise in custody shortfalls and the volume of cash and custody breaks that CASS controls then have to absorb.

The useful question for CASS is narrower than “did the US cope?”. It’s the same test we come back to later in this article: whether a shorter settlement window lets existing weakness in a firm’s own process surface faster than they do today. This could mean that controls, which currently work with an extra day’s headroom, will stop functioning once that buffer is removed after October 2027. Firms should have a view, based on their own evidence, on which of the fail-rate scenarios above they are more likely to face, rather than assuming the US result.

Reconciliations: same requirement, tighter overnight window

Nobody is proposing CASS reconciliations move intraday, and T+1 doesn’t create that requirement. The daily internal client money reconciliation under CASS 7.15.12R and CASS 7.15.15R(1) stays exactly as it is. What’s more likely to change is what the reconciliation finds when it runs. Under T+2, a settlement exception has an extra day to resolve before the reconciliation captures it as a break; under T+1, more exceptions could still be open when the reconciliation runs the following morning. That doesn’t change the control, but it changes how many breaks firms need to investigate, clear and/or include in its client money requirement.

Test it against your own data

A practical, low-cost exercise involves pulling six to twelve months of settlement failures and grouping them by root cause, such as bad Standard Settlement Instructions (SSIs), late allocations, funding gaps, securities availability, counterparty delays, and data errors. For each category, ask whether there would still have been enough time to resolve it under a T+1 clock before it touched a CASS-dependent process. That can help give an indication of where to prioritise, automation, earlier escalation, additional monitoring, based on actual known failures rather than a generic industry checklist.

One thing we'd flag from similar exercises elsewhere: this tends to work better run jointly with second-line risk rather than left entirely with Operations. Operations will find the process gaps; risk is more likely to catch where a gap actually reaches client money or custody assets, which is the distinction that matters for CASS.

Funding and third parties get less forgiving too

Faster settlement means funding needs to be in place sooner, and cross-border trades bring FX and time-zone pressure into that same tighter window. Where that touches client transactions, it's worth checking for knock-on effects on client money flows, client transaction accounts, or reliance on firm money to bridge settlement. Custodians, settlement agents, clearing brokers and banks are also changing their own cut-offs and exception processes for T+1, the question for CASS isn't just whether a custodian is ready, but whether anything they're changing quietly breaks an assumption a firm's CASS control depends on.

Test the failure, not just the clean settlement

Readiness testing that only rehearses successful settlement misses the point. Scenarios worth running include inaccurate or mistimed settlement instructions, including Place of Settlement (PSET) / Place of Safekeeping (PSAF) and other SSI data errors, delayed third-party data, funding shortfalls, securities lending recalls not returned in time to settle, a cluster of failures, or disruption near a critical cut-off. For each, it's worth tracing the path through. Consider what shows up in the books and records, whether there's a client money or custody consequence, which control catches it, who owns the escalation, and whether it's caught early enough to matter. Where settlement underpins an important business service, the same scenarios are also useful input to operational resilience testing, an outage doesn't get shorter just because settlement moved from T+2 to T+1, but the margin for recovering from it does.

Where this leaves CASS functions

The US experience is a reasonable basis for confidence that T+1 can be delivered. The FCA's current expectations are also clear that firms should be past planning and should now be into implementation and testing. For CASS functions specifically, the question isn't whether T+1 brings a new regime, it doesn't. It's whether controls that work today, with a day's more headroom than they'll have from October 2027, keep working once that headroom is gone. T+1 starts as an Operations programme. It becomes a CASS problem the moment an unresolved exception reaches client money or custody assets, and the firms best placed for 2027 are the ones that have already worked out where that moment is most likely to arrive.

A note on interpretation

The points above, which include earlier identification of CASS-relevant exceptions, sharper intraday monitoring, revisiting escalation thresholds, testing historical failures against T+1 timelines, are our analysis of where T+1 and existing CASS requirements interact. They are not new FCA requirements and shouldn't be read as FCA guidance directing firms to adopt these specific controls.