Cameron was speaking at Williams' Grove headquarters, where he officially opened the team's new Advanced Engineering facility.
"More races, more events, more money coming into our country and more success for this extraordinary industry," he said.
Cameron's news is a boost for events like the new electric single seater series Formula E, who are planning a street race in Battersea Park next year.
"The news is good," F1 chief executive Ecclestone agreed, "but I don't know whether you'd have street racing because it's not cheap to put on something that's safe.
"Street racing is expensive," he is quoted by the Daily Star.
"It just depends on what we can come up with commercially because how are we going to fund it?" he added.
"If they ever get it together then we'll see what happens. At least it's a good sign, a step in the right direction."
A spokesperson for London mayor Boris Johnson said: "He (Johnson) is positive that London would do a spectacular job of hosting a grand prix.
"But it is impossible to say what the impact might be without detailed planning and research and the question of air quality and noise impact would have to be looked at very carefully."