To understand the IBOR transition — arguably the most operationally complex regulatory programme ever imposed on the financial industry — you need to understand why LIBOR had to go. The manipulation scandal was the trigger, but the structural problems ran deeper. LIBOR was built on a model that had worked when interbank lending was active and banks were willing to transact; by the mid-2000s, that market had thinned dramatically, and the benchmark had become increasingly untethered from actual transactions.
The LIBOR Scandal: What Happened
LIBOR manipulation came in two forms. The first — rate-setting to benefit trading positions — involved traders at panel banks requesting that their LIBOR submitters set rates slightly higher or lower on particular days to benefit derivatives positions that were sensitive to the fixing. Internal messages showed traders explicitly requesting favourable submissions from colleagues responsible for the submissions process, sometimes in exchange for meals or favours. The manipulation was often small in basis-point terms, but with trillions of notional referencing LIBOR, even one or two basis points of mispricing across a fixing period generated significant profits.
The second form of manipulation — rate-setting to project financial health — emerged during the financial crisis. Banks under pressure in 2007 and 2008 were suspected of submitting artificially low LIBOR rates to avoid signalling funding stress to the market. A bank that submitted a high rate was implicitly saying it was struggling to borrow; submitting low, even if inaccurate, allowed it to maintain the appearance of normalcy. This form of manipulation involved the whole institution's reputation management, not just individual traders.
Barclays was the first bank to settle with regulators, paying fines to the US Department of Justice, the CFTC, and the FCA totalling $450 million in 2012. UBS, RBS, Deutsche Bank, Citigroup, JPMorgan Chase, and others followed. Total fines across institutions exceeded $9 billion. Several individuals were convicted of wire fraud and conspiracy in US and UK criminal proceedings.
The Wheatley Review
The UK government commissioned Martin Wheatley — then managing director of the FSA, shortly to become the first CEO of the FCA — to review LIBOR and recommend reforms. The Wheatley Review, published in September 2012, concluded that LIBOR could not be abolished immediately (too many contracts depended on it) but needed fundamental reform: the submission process had to be anchored in real transactions where possible, the panel had to be governed independently, and the criminal law had to be extended to cover LIBOR manipulation explicitly.
The reforms were implemented: LIBOR was brought under statutory regulation, the British Bankers' Association handed over administration to ICE Benchmark Administration, and criminal sanctions for benchmark manipulation were introduced in the UK. But as regulators assessed the reformed benchmark, the deeper structural problem became clear: the interbank unsecured lending market that LIBOR was supposed to measure had simply ceased to function at sufficient volumes to support a robust benchmark. Survey-based rates cannot be made robust by governance alone when the underlying market does not exist.
The FSB and the Global Reform Process
The Financial Stability Board (FSB), the international body coordinating financial regulation among G20 members, took charge of the global reform agenda. Its 2014 report on financial benchmarks recommended that interest rate benchmarks be anchored in actual transactions where feasible, with the development of risk-free rate alternatives to LIBOR where the transaction base was insufficient. The report launched the process that led to the selection of SONIA, SOFR, €STR, SARON, and TONA as the RFRs for GBP, USD, EUR, CHF, and JPY respectively.
National working groups were convened in each currency area. The UK's working group on sterling risk-free reference rates, co-chaired by the Bank of England and the FCA and comprising major market participants, worked through the selection criteria and ultimately recommended SONIA as the sterling RFR. A reformed SONIA was published from April 2018, capturing a broader set of overnight sterling transactions and calculated to a higher standard of transparency.
SONIA vs LIBOR: The Structural Differences
The differences between SONIA and GBP LIBOR are more than methodological — they reflect fundamentally different approaches to what a benchmark should measure.
Overnight vs Term
LIBOR was published for multiple tenors — overnight, one week, one month, two months, three months, six months, and twelve months. This term structure made it directly usable as a reference rate for instruments of any maturity without compounding. SONIA is an overnight rate. To construct a term equivalent, it must be compounded over the relevant period. This distinction has driven the need for new conventions, systems, and documentation across the entire market.
Secured vs Unsecured
GBP LIBOR measured unsecured interbank borrowing — the rate at which banks lent to each other without collateral. SONIA measures unsecured overnight sterling lending but captures a broader range of counterparties, including non-bank financial institutions. The unsecured nature of both means they incorporate some element of bank credit risk, unlike SOFR (which is based on secured repo transactions). The practical implication is that SONIA tends to be higher than a secured overnight rate during periods of financial stress, when bank credit premia rise.
The Credit Component
LIBOR's term structure embedded a bank credit risk premium: the three-month LIBOR rate reflected both the expected path of overnight rates over the next three months and the additional premium demanded by lenders for the credit risk of lending to a bank for three months unsecured. SONIA overnight does not have this term credit component — it reflects only the overnight lending rate, with no forward-looking bank credit premium. This difference — approximately the ISDA credit spread adjustment — matters for the economics of contracts that switch from LIBOR to SONIA, particularly those that previously relied on LIBOR's credit component to compensate lenders for bank credit risk.
SOFR: The US Parallel
While the UK developed SONIA as its RFR, the US chose the Secured Overnight Financing Rate (SOFR) as the replacement for USD LIBOR. SOFR is a fundamentally different beast from SONIA: it is based on overnight US Treasury repo transactions — secured lending — not unsecured lending. The repo market that underlies SOFR is vastly larger than the unsecured overnight market, making SOFR extremely robust and hard to manipulate. However, because it is secured, SOFR sits below an unsecured rate in normal conditions and may behave very differently from LIBOR in stress periods when secured and unsecured rates diverge sharply (as they did in September 2019, when SOFR spiked dramatically due to repo market technical pressures).
The USD transition was complicated by the size of the USD LIBOR market (much larger than GBP LIBOR), the diversity of market participants and products, and the debates about whether SOFR's secured nature made it unsuitable for certain credit-sensitive products — a debate that led to the emergence of credit-sensitive alternatives such as BSBY (now discontinued) and AMERIBOR. The Alternative Reference Rates Committee (ARRC) ultimately succeeded in driving SOFR adoption, with most new USD derivatives referencing SOFR by mid-2023 and USD LIBOR ceasing publication in June 2023.
The Lasting Impact
The IBOR transition reshaped global interest rate markets. It demonstrated that even deeply entrenched market standards — LIBOR had been in use for over thirty years and was the reference for virtually every floating rate instrument in major currencies — can be replaced when the political will exists and the regulatory pressure is sustained. It also demonstrated the enormous operational cost of such transitions: billions of dollars spent across the industry on system changes, legal documentation, client communication, and risk model recalibration. The lesson for future benchmark reforms is that the earlier transition planning begins and the clearer the regulatory timeline, the lower the ultimate cost to the system.