In recent weeks I have been canvassing in Wales, Scotland and many local authority areas in England. There is a widespread expectation that the efforts of Labour Scottish parliament and Welsh assembly members and councillors will be overshadowed as voters cast their ballot on the basis of Westminster politics. Yet a vote for Labour on Thursday is a vote against the worst excesses of New Labour in Westminster.

Without even having revenue-raising powers, the Welsh assembly has forged ahead with policies on education and health, resisting the marketisation seen in England: league tables and Sats have been abolished, and there are no city academies or trust schools; there are no foundation hospitals, and prescription charges have been abolished. In Scotland, care charges for the elderly have been abolished and there are no student top-up fees. Many Labour councils have similarly proud achievements. These are policies backed by most Labour members - and on which I am standing.

If we are to prevent the Tories returning to power we need to understand not only how New Labour has failed to live up to the hopes of the country in 1997, but also why. The leadership debate is as much a challenge for the Labour left as it is for New Labour. It provides an opportunity not just to demonstrate that the left has an understanding of the 21st-century globalised economy but also that it has the imagination to excite and mobilise our communities around an alternative vision and set of policies.

New Labour's leaders have adapted enthusiastically to the changes corporate-driven globalisation has effected, bringing the ideas and practices of the market into everyday life. All too often socialists and progressives have ceded ground to New Labour by being too defensive, even backward-looking. We cannot turn the clock back, but that does not mean we should accept the global market economy as the last word.

We need a new approach that deepens the quality of democracy throughout society, while establishing social rights to affordable housing, a citizen's income, free education, childcare and healthcare, as well as care in older age - in essence a new constitutional settlement for the 21st century. Such a debate would re-engage all those who since 1997 have not voted, and many young people.

In deciding not only the next Labour leader but also the next prime minister, the forthcoming contest is an opportunity to re-engage the British public in genuine political debate. That can only happen if there is a contest - and that can only be good for democracy.

· John McDonnell MP is a declared candidate for the Labour leadership and the author of Another World is Possible - a manifesto for 21st century socialism

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