The Tories said they will investigate claims that they had failed to declare the true sources of almost £40,000 of donations.
A series of cash gifts between 2005 and 2008 were registered with the Electoral Commission as coming from a company called Unicorn Administration.
According to The Sunday Times, however, the money had been paid by Unicorn on behalf of a number of donors including Zac Goldsmith, now the party's candidate for Richmond Park.
The other donors were said to be Mr Goldsmith's brother Ben and property developers the Reuben brothers.
While the Tories were apparently informed of the sources of the cash, which came in five different donations totalling £38,950, they were not registered as such with the Electoral Commission.
A Conservative Party spokesman said: "It appears that there may have been an administrative error in registering these donations.
"Now that it has been drawn to our attention, we are taking immediate steps to investigate it and rectify the declarations as necessary.
"Clearly, there was no motive of concealment since all those on whose behalf Unicorn was acting have already been declared as donating to the party."
Party sources insisted that there had been no attempt cover up the donations and that all of the donors were individually listed elsewhere on the Electoral Commission's register.
But Lord Oakeshott, a Liberal Democrat Treasury spokesman, said he would be asking the Electoral Commission to conduct an inquiry.
"Back-door gifts through front companies blatantly break the spirit of the law on cleaning up Britain's moneybags politics," he said.
"If the Conservative Party have nothing to hide, why not declare straight out their thousands instead of using the cover of Unicorn Administration? It is hard to see how these can be simple errors."