Libor, or London Interbank Offered Rate, is being replaced with rates compiled by central banks after lenders were fined billions of dollars for trying to rig what was once dubbed the world’s most important number, used for pricing a wide range of debt from home and company loans to credit cards.

“Today’s announcements mark the final chapter in the process that began in 2017, to remove reliance on unsustainable Libor rates and build a more robust foundation for the financial system,” Bank of England Governor Andrew Bailey said in a statement.

“With limited time remaining, my message to firms is clear – act now and complete your transition by the end of 2021.”

While the switch to rates compiled by central banks has proceeded well in derivatives, loans have lagged.

“Today’s announcement will put an end to any residual hopes for further delay in market transition to risk-free rates,” said Michael Cavers at law firm CMS, which is advising clients on the transition.

There are 35 Libor permuations across sterling, the euro, Swiss franc, yen and the dollar, with 26 ceasing on Dec. 31. Two dollar versions continue until mid-2023 for existing contracts, as previously announced by the U.S. Federal Reserve.

Britain’s Financial Conduct Authority (FCA) said that selected sterling, yen and perhaps dollar Libor permutations will continue in “synthetic” form after December for some existing contracts to be defined in a public consultation.

Despite many Libor rates being underpinned by few or no actual market transactions, the FCA said it does not expect any Libor setting to become “unrepresentative” before December. This avoids contracts having to switch to another rate at short notice.

“This is surprising in that it looks like a move to impose regulatory certainty upon commercial reality,” said Claude Brown, a lawyer at Reed Smith.

“Outside the U.S. dollar markets, this marks the end game.”