The move caused irritation in senior Liberal Democrat circles because it arose from a motion put to the conference by Evan Harris, the Health spokesman, rather than through usual policy channels.

One party official accused Dr Harris of trying to use the conference to bounce colleagues into accepting his spending aspirations before a bidding process for manifesto pledges. He said: “He (Dr Harris) is well aware in terms of specific policy that goes in the manifesto that he will bid for this, having established the general principle.”

Another close aide of Mr Kennedy predicted that free NHS prescriptions and dental treatment would be excluded from the manifesto, although it would remain formal party policy.

There was particular annoyance that the move would trigger accusations that Mr Kennedy wanted to raise taxes to fund the pledge, when he is trying to shed the party’s tax-and-spend image and has pledged not to increase the tax burden.

Although Dr Harris emphasised in his speech that the party was not calling for rises in overall taxation, his motion endorsed “the principle of taxing more fairly in order to end the charging of the sick . . . at the point of delivery”.

Dr Harris told the conference: “If you accept the principle of free at the point of delivery you must accept that charges for healthcare, which are effectively a tax on the sick and the elderly . . . are not logical, nor rooted in the principles of the NHS.”

Charges put a barrier in the way of patients receiving timely medical check-ups and so made preventative care more difficult, he said.

Dr Harris told The Times that abolishing NHS prescription charges would cost £430 million and ending payments for dental checks and treatment a further £470 million, but said there would be savings from scrapping inefficient collection costs.

The row has simmered behind the scenes during the week but his motion proved uncontroversial in the conference hall at Brighton and was carried overwhelmingly. Lib Dem policy is usually formed by a cumbersome procedure in which the federal policy committee appoints a working group to consult on and agree a paper with the relevant policy spokesman, who brings the document to the conference for approval.

Dr Harris did the opposite, setting out his plans in a motion submitted to the conference via his local party in Oxford West and Abingdon. Further details were published in a consultation paper hurriedly published last weekend.

Its timing coincided with the debate after the Brent East by-election over whether Mr Kennedy was taking his party to the left of Labour.

David Laws, a Treasury spokesman, illustrated the tensions over the proposals when he gave warning at a fringe meeting of the poor value for money of “old Labour policies of simplistic scrapping of each and every public sector user charge”.

Mr Laws said: “We need to carefully consider whether scarce financial resources are really best used in scrapping all user charges, even if that leaves us providing precisely the same services, while reducing the burdens on many of those who can already afford to pay.”

The Liberal Democrats’ main manifesto commitment on health policy has been to scrap personal care charges for the elderly, which the party estimates would cost £788 million a year. It would be financed from savings within the NHS budget, leaving little scope for efficienies to pay for a more costly pledge.

The 2001 manifesto also promised to abolish charges for eye tests and dental check-ups, but not payments for NHS dental treatment. Abolishing prescription charges has previously been an aspiration rather than a firm policy pledge.

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