Children in state schools could attend music, school and dance classes on a Saturday under proposals to extend the school week being considered by the Education Secretary.

Alan Johnson, who is tipped as the favourite to run against the Chancellor Gordon Brown for the Labour leadership, said Saturday lessons could " broaden horizons" for state-school pupils. "What you can do with Saturday schools is issues like the arts, music and dance, and broaden horizons," he said.

Mr Johnson is also "seriously considering" lifting the school leaving age from 16 to 18. In an interview with The Sunday Times, he said too many teenagers leave school without enough qualifications.

He disclosed that he would only run for the leadership of the Labour Party if there is a "clear consensus". But he said Gordon Brown was the "clear favourite" and said he had "huge admiration" for him. "He has said he would welcome a contest," Mr Johnson added. "That is a decision for the party to make and no doubt, when Tony steps down, a clear consensus will emerge on the best way forward."

Meanwhile, in an exclusive opinion poll for The Independent on Sunday, 59 per cent of voters asked said they think Labour is heading for defeat at the next general election. As a measure of the damage inflicted on the Government's image by recent events, 71 per cent of those questioned agreed that "the Labour leadership is split into warring factions" ­ a view held by 61 per cent of Labour voters.

The poll also reveals strong support for the idea that Gordon Brown should face a challenge for the top job. Sixty-four per cent ­ and 57 per cent of Labour voters ­ agreed that "if Brown takes over without a leadership contest, the British people will feel cheated".

The findings are a boost to the hopes of John Reid, the Home Secretary, who has started to assemble a campaign team to run against Mr Brown and has secretly enlisted a wealthy businessman and a former Labour Party chief. Officially, Waheed Alli, the media entrepreneur ennobled in 1997, and Margaret McDonagh, Labour's former general secretary, are acting as " unpaid, unofficial advisers" on Mr Reid's overhaul of the Home Office. In fact, both are helping to prepare a challenge for the top job, according to allies.

When the IoS poll, carried out last week by CommunicateResearch, asked if "the Labour Party treated Tony Blair badly by forcing him to say he would step down within a year", 55 per cent agreed. And, while 51 per cent of all voters agree that "there is no point in Tony Blair staying on as Prime Minister beyond Christmas", 59 per cent of Labour voters want him to carry on.

CommunicateResearch interviewed 1,013 people by phone on 20 and 21 September. Details at www.communicate research.com