The Prime Minister tried to answer trade union criticism of Government policies when he gave a relaxed, 20-minute speech at a private dinner with the TUC.
Gordon Brown cracked jokes and attacked the Conservatives when he joined senior union leaders at a dinner in Brighton.
He was warmly received at the dinner but union officials said later they wanted to see evidence that he understood the scale of the difficulties Labour faced.
Tony Woodley, joint leader of Unite said the "jury was out" on whether the Prime Minister could turn around the fortunes of the Government in the coming months.
"There is no doubt Gordon Brown is a decent person and I accept the economy is a world problem but the question is - what is the Government going to do about it.
"If he is going to do something he has to act by the time he addresses the Labour Party conference in two weeks."
Mr Woodley said Mr Brown appeared "friendly and relaxed" and delivered his speech without notes, speaking off the cuff.
More than a dozen members of the Cabinet joined Mr Brown at the dinner, including Schools Secretary Ed Balls, Foreign Secretary David Miliband and Chancellor Alistair Darling.
Mr Brown told the union officials that he will be announcing in the next few days an initiative aimed at cutting the fuel bills of families across the country believed to involve insulating homes to improve energy efficiency as well as creating new jobs.
He attacked the Conservative Party's policies announced in recent weeks which he said favoured high earners and would include cutting public spending.
The politicians and union leaders tucked into a three course meal including starters of Bayonne ham, plum tomato and buffalo mozzarella, a main course of chicken, tarragon, shallots and white wine cream, and a dessert of baked black cherry and almond flan followed by coffee and a chocolate truffle.