Baroness Billingham, who is also president of the Oxfordshire Lawn Tennis Association, said US Open champion and Olympic gold medallist Andy Murray, and silver medallist Laura Robson, had succeeded regardless of the national organisation.
Labour's Culture, Media and Sport spokeswoman hit out after the LTA told a House of Lords committee on Olympic and Paralympic legacy that increasing participation was "at the heart of what we do" and it had aimed to use the Games to identify and support talent.
But Baroness Billingham, a long-standing critic of the organisation, said she did not accept the claims.
"I don't think you have increased participation," she told the committee. "I don't think you can claim accreditation for Andy Murray and Laura because they came from outside the system.
"I have to say that my view is shared by Sport England, who have cut your funding because they think you are inadequate and, indeed, by the sports minister.
"Having, in my view, a very poor legacy, what are your plans now to put that right? I understand you are appointing a new chief executive officer. Now, I heard this morning the criteria for his appointment is going to be that he's good with money.
"As Tim Henman said well, we'd like somebody who is good with tennis."
She added: "Just one last reminder that in 2005 your chief executive, who was then Roger Draper, promised us that by 2010 we would have at least 20 men in the the top 100 so your pious hopes really don't ring very strong with me."
James Munro, the LTA communications director, told peers that 2012 had been the "best year" for the sport in his lifetime.
He said initiatives carried out by the organisation had increased the number of students involved in the sport and overall adult participation had increased by 18 per cent.
Pressed by the Labour peer, he added: "We recognise that we have a long way to go but I think, probably, one of the great legacies for us out of the Olympic and Paralympic Games is that we are fully focused and our mission is to get more people playing tennis."