After going from crunch talks on the issue in Brussels to a Commonwealth summit in Perth, Cameron said the 17-member eurozone bloc "quite rightly" needed to push ahead with its own actions, including separate extra meetings.
But he added: "As I've said many times, it's important that we safeguard the single market of the 27. That is our key national interest. That Britain, a historic trading nation, has its biggest markets open.
"That's the point I made with the European Council on Sunday, and again on Wednesday and I am sure when we have the next one I will be making it again."
"And there are other members not in the euro who care very deeply about the single market and agree with this approach," he added during a joint press conference with Australian Prime Minister Julia Gillard.
The British leader cancelled planned trips to New Zealand and Japan to attend the EU meeting on Wednesday but arrived in time for the start of the Commonwealth Heads of Government Meeting in Perth.
Cameron had previously warned that countries outside the eurozone risked being frozen out amid efforts for a pooled response to the crisis crippling the 17-nation single currency bloc.