The Tories say they will investigate the handling of the Goldsmith donations
The Conservative Party has admitted making mistakes in registering the true source of a number of donations, totalling nearly £40,000.
The Electoral Commission was told the money had come from a company called Unicorn Administration.
But the company was acting on behalf of a number of people including Zac Goldsmith, the party's candidate for Richmond Park, the Sunday Times says.
A Tory party spokesman said it was due to an administrative error.
The other donors of a series of cash gifts between 2005 and 2008 were said to be Mr Goldsmith's brother Ben and property company Motcomb Estates.
While the Tories were apparently informed of the sources of the cash, five different donations totalling £38,950, they were not registered as such with the Electoral Commission.
'Back door gifts'
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 to cover up the donations and that all of the donors were individually listed elsewhere on the Electoral Commission's register.
Liberal Democrat Treasury spokesman Lord Oakeshott 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."