The TUC general secretary has warned Britain's unions that they should not reject the proposed European Union constitution out of hand.

In an article published in this week's Tribune newspaper, Brendan Barber says that workers should judge the document by what it says, rather than what the government's negotiating position was.

Key unions, including the powerful Transport and General Workers Union, have indicated they could oppose the treaty when the government holds a referendum on it.

They have been angered by the government's refusal to accept provisions in the constitution that could give more power to trade unions.

Tony Woodley, TGWU general secretary, has said the government's approach is "making it all but impossible for trade unionists to support a 'yes' vote in a referendum".

And Barber warned that there was "real anger" about the government's actions.

However, he urged the traditionally pro-European union movement not to deliver an outright "no" to the constitution.

"There are certainly some good things in the final document," he said.

"Proposals for an EU foreign minister for example will appeal to those who want Europe to challenge US foreign policy more effectively when it is acting unilaterally or on a neo-con agenda.

"Importantly the constitution commits the EU to operating through a process of social dialogue, and it gives a special and guaranteed role to the social partners.

"Unions are therefore given permanent access to decision making - rather different than our experience of the long nightmare of Thatcherism."

And he adds that the controversial European charter of fundamental rights will not do as little for unions as the government claims.

"We will not like some of the government's arguments for a yes vote in the referendum," he said.

"If they lose it will undoubtedly harm them, and some may well say that serves them right.

"On the other hand it will also boost almost every interest group and political stance that is hostile to trade unionism and the European social model."

He reminded unions that the constitution "talks of social dialogue and full employment".

"If unions decide on balance that we will support the constitution, we will reserve our right to put a distinct trade union argument, and not be subsumed into a government and business led campaign," he added.

"We want a people's Europe, not one just for business and bankers. That will continue to be our guiding principle. If that makes us awkward allies for a yes campaign, then so be it."