Banks including HSBC Holdings Plc, Barclays Plc and NatWest Group Plc have only passed through about a quarter of interest rate rises to savers, the Financial Conduct Authority said as it warned of “robust action” for firms that don’t transfer benefits to consumers.

Nine of Britain’s biggest lenders such as Lloyds Banking Group, Banco Santander SA and Virgin Money UK Plc passed on an average of 28% of base rate rises between January and May in their instant access savings offers, compared with an average of 80% in the five years through 2009, the FCA said in a report on Monday.

With the Bank of England lifting rates 13 times from almost zero in the past two years in an attempt to tackle inflation, lenders are under increasing scrutiny over how they feed this into the savings market. Banks are also facing pressure to ensure access to financial services more broadly, after NatWest’s decision to close Nigel Farage’s account sparked a political firestorm that led to Alison Rose resigning as chief executive officer last week.

Sheldon Mills, executive director of consumers and competition at the regulator, told reporters he supported NatWest Chairman Howard Davies, who has said he’ll remain in post to handle the repercussions of Rose’s departure despite some political pressure to quit. Mills said the question of whether Davies should stay was ultimately for NatWest’s board, but he added he would urge board members “to achieve stability within that institution.”

‘Moving Feast’

The FCA also introduced a long-planned consumer duty on Monday that requires banks to ensure they act in the best interests of retail customers on a range of issues.

Lenders in the UK have so far reported rising earnings in the first half of the year, though several have also warned that the improvement in margins from rising interest rates was already slowing.

Read more: Barclays Shares Drop as UK Lender Signals End of Rates Boom

From the end of August, firms offering the lowest savings rates will have to justify how they offer fair value under the new consumer duty, the FCA said. By the end of the year it will take “robust action” against firms that can’t demonstrate such value.

“We will be taking significant supervisory steps to ensure firms are getting on with this,” Mills said. “If we see low savings rates and those continue we’ll work with banks to make our views known and will consider what actions to take.”

The FCA will publish a list of firms’ instant-access savings rates every six months, ranking them from best to worst.

A spokesperson for Lloyds said the bank offered “a range of accounts customers can choose from depending on the flexibility they want,” with rates as high as 6.25% on its monthly saver account. “We have actively been contacting over 10 million customers about their options,” they added.

Representatives for the other banks didn’t immediately respond to emailed requests for comment.

“Consumers should shop around for the best rates but loyal savers should not be penalized,” Harriett Baldwin, chair of the Treasury committee, said in a statement. The committee has called in bank bosses this year to defend their savings rates.

Banks have spent almost two years preparing for their new obligations under the consumer duty. The regime is set to be “a moving feast for regulatory professionals from firm to firm,” according to Claire Carroll, partner at law firm Eversheds Sutherland. “Every firm has to evaluate their business model and base their response to consumer duty on those factors.”

As of May, 60% of deposits from the nine firms were held in instant access accounts. Banks have been transferring rate rises more successfully on noticed and fixed-term deposits, with the pass-through rate reaching 51%. The FCA said firms need to step up communications with customers about their options and a measure the effectiveness of this.

“We want a competitive cash savings market that delivers better deals for savers, where interest rates are reviewed quickly following base rate changes,” the FCA said in a statement. “We continue to urge savers to shop around.”

(Updates to add Lloyds response in tenth paragraph.)