The move is a response to what Mr Hague sees as the government's mishandling of health service priorities.

The Tory leader says there are "countless examples" of patients suffering because clinical priorities are being distorted by Labour's pledge to tackle NHS waiting lists.

During a visit to Chelsea and Westminster hospital, he said: "The prime minister is obsessed with waiting lists.

"As far as he is concerned the NHS exists to enable him to meet his headline-grabbing but ill-advised election pledge whatever the consequence.

"He doesn't seem to care if patients receive the treatment they need when they need it."

Mr Hague made his pledge while accompanying Michael Portillo, the Tory candidate for the Kensington and Chelsea by-election.

William Hague is hitting the campaign trial

The announcement forms part of what the Tories are calling the patients' guarantee, another pledge in their "commonsense revolution".

Under this initiative, Mr Hague said the most important conditions should be treated first.

The visit comes as nominations have closed for candidates to stand in the by-election scheduled for 25 November.

The poll was caused by the death of the Conservative MP and diarist Alan Clark.

The seat is one of the safest Conservative constituencies in the country.

The Labour Party candidate is Robert Atkinson, the leader of the Labour group on the local council, who contested the seat at the general election for the party.

The Liberal Democrat candidate is Robert Woodthorpe Brown, also a former councillor.

The full list of candidates:

• Labour: Robert Atkinson
• Liberal Democrats: Robert Woodthorpe Browne
• Green Party: Hugo Charlton
• Independent Environmentalist Stop Climate Change: John Davies
• Democratic Party: Charles, Earl of Burford
• UK Independence Party: Damian Hockney
• Daily and Sunday Sport Party: Louise Hodges
• Official Monster Raving Loony Party: Alan "Howling Laud" Hope
• Campaign for Living Will Legislation: Michael Irwin
• People's net dream ticket Party: Lisa Lovebucket
• Equal Parenting Party: Peter May
• UK Pensioners Party: George Oliver
• Legalise Cannabis Alliance: Colin Paisley
• Conservative: Michael Portillo
• Referendum Party: Stephen Scott-Fawcett
• Pro Euro Conservative Party: John Stevens
• Stop Tobacco Companies Farming Our Children: Tonysamuelsondotcom
• Natural Law: Gerard Valente.