David Cameron could be the first Conservative leader to address the TUC conference as part of a "beer and sandwiches offensive" to woo the union movement.
The Tory leader has appointed a personal trade union envoy to extend his appeal beyond core voters. It paves the way for him to take to the TUC platform as early as next year – breaking the exclusive link Labour has enjoyed with the union movement for decades.
Richard Balfe, a former Labour MEP, will have a wide-ranging remit to talk to general secretaries and sell the Tory message to the more than eight million union members in the UK. He will also develop relations with co-operatives.
No Conservative leader has addressed the TUC in its 144-year history, but aides said Mr Cameron would be happy to speak, if asked. The TUC said there were "no plans" for an invitation to this autumn's congress, but a source said: "We never rule anything out because there could be a time in the foreseeable future when he is Prime Minister."
If the Conservatives win a 2009 election, Mr Cameron could address unionists that September.
The bridge-building will be seen as a symbolic equivalent of Tony Blair's ditching of Labour's Clause 4 commitment to public ownership – a device he used to show his party had across-the-board appeal. It also distances Mr Cameron's Conservative Party from Margaret Thatcher's anti-union legislation.
The "beer and sandwiches" push mirrors the "prawn cocktail offensive" launched by Labour in the early 1990s to reassure the City that the economy would be safe in its hands.
Mr Cameron told The Independent on Sunday: "I am delighted that Richard Balfe is going to help develop our relations with the trade union and co-operative movement. I have always said that free enterprise and the co-operative principle are partners, not adversaries, and co-operatives have an important role to play in public service reform by bringing dynamism without the loss of public ethos."
Aides insisted it was not a lurch to the left but a sign that the Conservative leader was broadening his reach to prepare for government.
But the appointment could backfire by angering traditional Tories while repelling some union leaders on the left. Bob Crow, general secretary of the RMT rail workers' union, said: "What we find difficult to believe is that general secretaries would be stupid enough to be embroiled in some kind of publicity stunt. It would be completely ridiculous to have Cameron addressing the conference. The Tories are the authors of the anti-union legislation which is the principal thing tying the hands of the unions today. It is only a short period of time since the Thatcher government. It is the same party, with the same policies against the trade unions."
A Unite source said: "We are a Labour-affiliated union, pure and simple. Very very clearly, we are wedded to them constitutionally."
Most unions, however, are not affiliated to Labour and nearly a third of union members vote Tory. Amicus, half of the super-union Unite, counts many middle managers among its membership. Labour leaders are given an automatic platform at the TUC every year. Tory ministers have been allowed to attend in the past but have been restricted to private TUC events.
The TUC general secretary, Brendan Barber, has in the past welcomed Mr Cameron's comments on fairer public sector pay, flexible working and childcare.
Mr Balfe said: "Around 30 per cent of trade union members vote Conservative, and under David Cameron's leadership the Conservative Party has shown that it has the ideas and vision to harness the co-operative movement in a way that can really benefit society. I want to show that we in the Conservative Party want to listen to and learn from these two valuable partners in society."
Mr Balfe has been a co-operative movement member since he was 16 and a union member since 1983. He was a Labour MEP between 1979 and 2001 before defecting to the Tories after that year's election.
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