The claim comes despite the Bank of England cutting its main interest rate to a record low of just 1.5%.
Tory housing spokesman Grant Shapps said it was "obscene" that some of the country's most vulnerable households were paying high interest at such a time.
He said a Conservative government would take action to create more competition in the home credit market.
The market is estimated to be worth £3bn a year but is dominated by just six companies.
Forcing companies to conform to the same data-sharing standards applied in the mainstream banking sector would allow consumers to switch more easily between lenders, said Mr Shapps.
Tory plans for a free National Finance Advice Scheme would also help consumers choose cheaper borrowing options - like Credit Unions.
The plans follows research suggesting that as many as 79% of consumers did not understand vital terms like APR (annual percentage rate).
Home credit companies typically offer "payday" loans to tide people over periods of financial pressure.
Loans rarely exceed £1,000 and are usually paid back in instalments within three months.
Companies are often ready to make decisions within minutes and extend loans to people with less-than-perfect credit histories.
But borrowers taking out a loan of £200 for one month often find themselves paying back £250 or £300 - the equivalent of an APR of well over 1,000%.
Mr Shapps's report cited one company, QuickQuid, whose website states that "depending on the loan term, typical APRs will range from 1351.7% to 9889.3%".