Brown's government is struggling to find a rescuer for stricken mortgage lender Northern Rock, a casualty of the global credit crisis, and is under pressure over a series of blunders.
One poll on Sunday showed the Conservatives extending their lead over the ruling Labour Party to 10 percentage points, though Brown does not have to call an election until 2010.
Brown, who is due to meet the leaders of France, Germany and Italy on January 29 to discuss the credit crisis, said more must be done to "ensure continued stability and to strengthen and deepen economic reform in Europe."
Now that the Lisbon Treaty has been signed, Europe must focus on stability, growth, competitiveness and jobs, he said.
Britain's parliament is set for a battle in the next few months on whether to ratify the treaty.
In 2005, the government promised a referendum on the proposed EU constitution, which was then rejected by French and Dutch voters. Brown sees no need for a referendum on its modified successor, the Lisbon Treaty, saying it does not involve a significant loss of sovereignty.
The Conservatives accuse him of betraying voters, and have refused to say whether a future Conservative government would accept the treaty, even if parliament had ratified it.
"We will not be content to rest at that point ... but I don't want to explain exactly what we'd do in those circumstances," Cameron said in a BBC interview on Sunday.
He said London had already transferred too much power to Brussels and it would be better if social and employment policy were decided in Britain rather than Brussels.
Brown has said that if the Conservatives were to hold a referendum after the parliament had ratified the treaty, it would amount to renegotiating Britain's EU membership.
