Moneyfacts says it believes taxpayer-backed banks are placing higher priority on getting out of government ownership rather than passing on competitive rates to the taxpayer.
RBS performed well, while others such as Cheltenham and Gloucester, Halifax and Northern Rock have struggled to meet the same grade, according to the figures.
RBS offered the most competitive rates of those in the survey between March 2009 and March 2010, with two-year fixes ranging from 3.27 per cent to 4.04 per cent, while Northern Rock and Halifax peaked with rates of over 5 per cent at times during the period.
Moneyfacts.co.uk press officer Michelle Slade says: “The large amount of money that has been pumped into some well known banks is still a sticky point with many British taxpayers.
“Many hoped that the state owned banks would be at the front of the queue for unlocking the mortgage market, but this isn’t the case.
“Some state-funded banks appear to place a higher priority on getting out of Government ownership, rather than helping with competitive rates the customers who supported them.”