The credit card issuer, which has 10 million customers, said that the link with the Bank of England base rate, which is likely to remain at its record 0.5% low for some time, will be severed.
Cardholders with rates that track the base rate will be put on "variable interest rates" from September in a move which has emerged just days after forward guidance from the Bank under new governor Mark Carney appeared to push back market expectations that rates could start rising as soon as next year.
Barclaycard's letters highlight the fact that the changes come about at a time when the Bank's base rate is at an "all-time low".
Credit card rates have been edging up in recent months and reached a high point of 19.1% in April, according to financial information website Moneyfacts, which started tracking APR (annual percentage rate) figures in 2007. They have slipped back slightly since to average 18.9%.
Rachel Springall, spokeswoman for Moneyfacts, said the changes could spell higher rates of interest for borrowers.
She said that Sainsbury's Cashback Low Rate MasterCard currently charges a market-leading low purchase rate of 7.8% APR.
However, she cautioned that applicants need to be mindful that the advertised APR only needs to be given to 51% of successful applicants, meaning people might not get the rate they had applied for.
Figures recently released by the UK Cards Association showed that online debit card spending overtook credit card spending for the first time last year.
Some 61% of adults have a credit card and the number of credit cards has held steady since 2005 at around 30 million.
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